Merge pull request #32 from Thales1330/wip/controller-solver

Wip controller solver

28 files changed, 702 insertions, 80 deletions

diff --git a/Project/ChartView.cpp b/Project/ChartView.cpp
index 199060a..2f3f70d 100644
--- a/Project/ChartView.cpp
+++ b/Project/ChartView.cpp
@@ -45,6 +45,8 @@ ChartView::~ChartView() {}
 void ChartView::SetMPWindow()
 {
     m_mpWindow = new mpWindow(this, wxID_ANY);
+    
+    m_mpWindow->SetDoubleBuffered(true);
 
     m_mpWindow->SetMargins(20, 10, 40, 60);
     m_xaxis = new mpScaleX("", mpALIGN_BOTTOM, true);
diff --git a/Project/ChartView.h b/Project/ChartView.h
index b40a63d..741ffe2 100644
--- a/Project/ChartView.h
+++ b/Project/ChartView.h
@@ -54,7 +54,7 @@ class ChartView : public ChartViewBase
     mpInfoCoords* m_coords = NULL;
     mpInfoLegend* m_leg = NULL;
 
-    bool m_hideGrid = false;
+    bool m_hideGrid = true;
     bool m_showLeg = false;
     bool m_showCoords = false;
     bool m_darkTheme = false;
diff --git a/Project/ConnectionLine.h b/Project/ConnectionLine.h
index e9d238a..98e3098 100644
--- a/Project/ConnectionLine.h
+++ b/Project/ConnectionLine.h
@@ -29,6 +29,9 @@ class ConnectionLine : public ControlElement
     virtual bool SetParentLine(ConnectionLine* parent);
 
     virtual std::vector<ConnectionLine*> GetLineChildList() const;
+    
+    virtual double GetValue() const { return m_value; }
+    virtual void SetValue(double value) { m_value = value; }
 
    protected:
     double m_lineOffset = 0.0;
@@ -38,6 +41,8 @@ class ConnectionLine : public ControlElement
 
     ConnectionLineType m_type = ELEMENT_ELEMENT;
     ConnectionLine* m_parentLine = NULL;
+    
+    double m_value;
 };
 
 #endif  // CONNECTIONLINE_H
diff --git a/Project/ControlEditor.cpp b/Project/ControlEditor.cpp
index 27c5662..12a9bd1 100644
--- a/Project/ControlEditor.cpp
+++ b/Project/ControlEditor.cpp
@@ -16,6 +16,8 @@
 #include "Constant.h"
 #include "Gain.h"
 
+#include "ControlElementSolver.h"
+
 #include "ChartView.h"
 #include "ElementPlotData.h"
 
@@ -617,35 +619,73 @@ void ControlEditor::OnKeyDown(wxKeyEvent& event)
             {
                 RotateSelectedElements(event.GetModifiers() != wxMOD_SHIFT);
             } break;
-            case 'L':
-            {
-                //tests
+            case 'L': {
+                // tests
                 if(event.ControlDown() && event.ShiftDown()) {
-                    std::vector<double> time, sinC, cosC, tgC;
-                    for(int i=0; i<360; ++i) {
-                        time.push_back(i);
-                        sinC.push_back(std::sin(wxDegToRad(i)));
-                        cosC.push_back(std::cos(wxDegToRad(i)));
-                        tgC.push_back(std::tan(wxDegToRad(i)));
+                    double timeStep = 1e-4;
+                    double integrationError = 1e-5;
+                    double simTime = 10.0;
+                    double printStep = 1e-3;
+                    double pdbStep = 1e-1;
+
+                    double pulsePer = 5.0;
+
+                    wxProgressDialog pbd(_("Test"), _("Initializing..."), 100, this,
+                                         wxPD_APP_MODAL | wxPD_AUTO_HIDE | wxPD_CAN_ABORT | wxPD_SMOOTH);
+                    pbd.SetDoubleBuffered(true);
+                    ControlElementSolver solver(this, timeStep, integrationError, false, 0.0);
+                    if(solver.IsOK()) {
+                        bool simStopped = false;
+                        double currentTime = 0.0;
+                        double printTime = 0.0;
+                        double pulseTime = 0.0;
+                        double pdbTime = 0.0;
+                        std::vector<double> time;
+                        std::vector<double> solution;
+                        std::vector<double> inputV;
+                        while(currentTime <= simTime) {
+                            double input = 0.0;
+                            if(pulseTime >= pulsePer * 2.0) pulseTime = 0.0;
+                            if(pulseTime >= pulsePer) input = 1.0;
+
+                            solver.SolveNextStep(input);
+                            if(printTime >= printStep) {
+                                time.push_back(currentTime);
+                                solution.push_back(solver.GetLastSolution());
+                                inputV.push_back(input);
+                                printTime = 0.0;
+                            }
+                            if((pdbTime > pdbStep)) {
+                                if(!pbd.Update((currentTime / simTime) * 100,
+                                               wxString::Format("Time = %.2fs", currentTime))) {
+                                    pbd.Update(100);
+                                    simStopped = true;
+                                    currentTime = simTime;
+                                }
+                                pbd.Refresh();
+                                pbd.Update();
+                                pdbTime = 0.0;
+                            }
+                            printTime += timeStep;
+                            currentTime += timeStep;
+                            pulseTime += timeStep;
+                            pdbTime += timeStep;
+                        }
+                        if(!simStopped) {
+                            std::vector<ElementPlotData> epdList;
+                            ElementPlotData curve1Data(_("TESTES"), ElementPlotData::CT_BUS);
+                            curve1Data.AddData(inputV, _("Entrada"));
+                            curve1Data.AddData(solution, _("Saida"));
+                            epdList.push_back(curve1Data);
+
+                            ChartView* cView = new ChartView(this, epdList, time);
+                            cView->Show();
+                        }
+                    } else {
+                        wxMessageDialog msgDialog(this, _("It was not possible to solve the control system"),
+                                                  _("Error"), wxOK | wxCENTRE | wxICON_ERROR);
+                        msgDialog.ShowModal();
                     }
-                    std::vector<ElementPlotData> epdList;
-                    
-                    ElementPlotData curve1Data(_("Func. polinomiais 1"), ElementPlotData::CT_BUS);
-                    curve1Data.AddData(sinC, _("seno"));
-                    epdList.push_back(curve1Data);
-                    
-                    ElementPlotData curve2Data(_("Func. polinomiais 2"), ElementPlotData::CT_BUS);
-                    curve2Data.AddData(tgC, _("tangente"));
-                    epdList.push_back(curve2Data);
-                    
-                    ElementPlotData curve3Data(_("Func. polinomiais 3"), ElementPlotData::CT_SYNC_GENERATOR);
-                    curve3Data.AddData(sinC, _("seno"));
-                    curve3Data.AddData(cosC, _("cosseno"));
-                    curve3Data.AddData(tgC, _("tangente"));
-                    epdList.push_back(curve3Data);
-                    
-                    ChartView* cView = new ChartView(this, epdList, time);
-                    cView->Show();
                 }
             }
         }
@@ -771,21 +811,19 @@ void ControlEditor::OnImportClick(wxCommandEvent& event)
                                   wxOK | wxCENTRE | wxICON_ERROR);
         msgDialog.ShowModal();
     }
-    
-    //Get the highest id number
+
+    // Get the highest id number
     int majorElementID = 0;
     for(auto it = m_elementList.begin(), itEnd = m_elementList.end(); it != itEnd; ++it) {
         ControlElement* element = *it;
-        if(element->GetID() > majorElementID)
-            majorElementID = element->GetID();
+        if(element->GetID() > majorElementID) majorElementID = element->GetID();
     }
     for(auto it = m_connectionList.begin(), itEnd = m_connectionList.end(); it != itEnd; ++it) {
         ConnectionLine* line = *it;
-        if(line->GetID() > majorElementID)
-            majorElementID = line->GetID();
+        if(line->GetID() > majorElementID) majorElementID = line->GetID();
     }
     m_lastElementID = ++majorElementID;
-    
+
     Redraw();
     event.Skip();
 }
diff --git a/Project/ControlEditor.h b/Project/ControlEditor.h
index 232ebd8..9de5a1f 100644
--- a/Project/ControlEditor.h
+++ b/Project/ControlEditor.h
@@ -9,6 +9,8 @@
 #include <GL/gl.h>
 #include <GL/glu.h>
 
+#include <wx/progdlg.h>
+
 #include "IOControl.h"
 
 class FileHanding;
@@ -25,6 +27,8 @@ class Exponential;
 class Constant;
 class Gain;
 
+class ControlElementSolver;
+
 class ChartView;
 class ElementDataObject;
 
diff --git a/Project/ControlElement.cpp b/Project/ControlElement.cpp
index fa99206..8df534a 100644
--- a/Project/ControlElement.cpp
+++ b/Project/ControlElement.cpp
@@ -121,3 +121,9 @@ void ControlElement::Move(wxPoint2DDouble position)
         m_nodeList[i]->Move(position);
     }
 }
+
+bool ControlElement::Solve(double input, double timeStep)
+{
+    m_output = input;
+    return true;
+}
diff --git a/Project/ControlElement.h b/Project/ControlElement.h
index 1cf4e0b..1e60f97 100644
--- a/Project/ControlElement.h
+++ b/Project/ControlElement.h
@@ -5,7 +5,7 @@
 
 class Node
 {
-public:
+   public:
     enum NodeType { NODE_IN = 0, NODE_OUT };
 
     Node(wxPoint2DDouble position = wxPoint2DDouble(0, 0), NodeType nodeType = NODE_IN, double borderSize = 0.0);
@@ -13,39 +13,33 @@ public:
 
     wxRect2DDouble GetRect() const { return m_rect; }
     void SetRect(wxRect2DDouble rect) { m_rect = rect; }
-
     wxPoint2DDouble GetPosition() const;
     void SetPosition(wxPoint2DDouble position);
 
     NodeType GetNodeType() const { return m_nodeType; }
     void SetNodeType(NodeType nodeType) { m_nodeType = nodeType; }
-
     double GetRadius() const { return m_radius; }
     std::vector<wxPoint2DDouble> GetInTrianglePts() const { return m_triPts; }
-    
     double GetAngle() const { return m_angle; }
     void SetAngle(double angle) { m_angle = angle; }
-    
     void Rotate(bool clockwise = true);
-    
+
     void RotateTriPt(double angle);
 
     void StartMove(wxPoint2DDouble position);
     void Move(wxPoint2DDouble position);
     bool Contains(wxPoint2DDouble position) const;
-    
+
     bool IsConnected() const { return m_connected; }
     void SetConnected(bool connected = true) { m_connected = connected; }
-    
     int GetID() const { return m_id; }
     void SetID(int id) { m_id = id; }
-
-protected:
+   protected:
     int m_id = -1;
-    
+
     wxRect2DDouble m_rect;
     NodeType m_nodeType;
-    
+
     bool m_connected = false;
 
     wxPoint2DDouble m_moveStartPt;
@@ -58,7 +52,7 @@ protected:
 
 class ControlElement : public Element
 {
-public:
+   public:
     ControlElement(int id);
     ~ControlElement();
 
@@ -67,11 +61,17 @@ public:
 
     void SetNodeList(std::vector<Node*> nodeList) { m_nodeList = nodeList; }
     std::vector<Node*> GetNodeList() const { return m_nodeList; }
-
     virtual void DrawNodes() const;
 
-protected:
+    virtual bool IsSolved() const { return m_solved; }
+    virtual void SetSolved(bool solved = true) { m_solved = solved; }
+    virtual bool Solve(double input, double timeStep);
+    virtual double GetOutput() const { return m_output; }
+    virtual void SetOutput(double output) { m_output = output; }
+   protected:
     std::vector<Node*> m_nodeList;
+    bool m_solved = false;
+    double m_output = 0.0;
 };
 
-#endif // CONTROLELEMENT_H
+#endif  // CONTROLELEMENT_H
diff --git a/Project/ControlElementContainer.cpp b/Project/ControlElementContainer.cpp
index f5372a8..e461529 100644
--- a/Project/ControlElementContainer.cpp
+++ b/Project/ControlElementContainer.cpp
@@ -2,7 +2,7 @@
 #include "ControlEditor.h"
 #include "ControlElement.h"
 
-ControlElementContainer::ControlElementContainer() {}
+ControlElementContainer::ControlElementContainer() { ClearContainer(); }
 ControlElementContainer::~ControlElementContainer() {}
 void ControlElementContainer::FillContainer(ControlEditor* editor)
 {
@@ -47,7 +47,8 @@ void ControlElementContainer::ClearContainer()
     m_tfList.clear();
 }
 
-void ControlElementContainer::FillContainer(std::vector<ControlElement*> controlElementList, std::vector<ConnectionLine*> connectionLineList)
+void ControlElementContainer::FillContainer(std::vector<ControlElement*> controlElementList,
+                                            std::vector<ConnectionLine*> connectionLineList)
 {
     m_ctrlElementsList = controlElementList;
     m_cLineList = connectionLineList;
diff --git a/Project/ControlElementSolver.cpp b/Project/ControlElementSolver.cpp
new file mode 100644
index 0000000..e67cb9a
--- /dev/null
+++ b/Project/ControlElementSolver.cpp
@@ -0,0 +1,263 @@
+#include "ControlElementSolver.h"
+
+#include "ControlElementContainer.h"
+#include "ControlEditor.h"
+#include "ConnectionLine.h"
+#include "Constant.h"
+#include "Exponential.h"
+#include "Gain.h"
+#include "IOControl.h"
+#include "Limiter.h"
+#include "Multiplier.h"
+#include "RateLimiter.h"
+#include "Sum.h"
+#include "TransferFunction.h"
+
+ControlElementSolver::ControlElementSolver(ControlEditor* controlEditor,
+                                           double timeStep,
+                                           double integrationError,
+                                           bool startAllZero,
+                                           double input)
+{
+    m_ctrlContainer = new ControlElementContainer();
+    m_ctrlContainer->FillContainer(controlEditor);
+
+    // Check if the sistem have one input and one output
+    bool fail = false;
+    wxString failMessage = "";
+    auto ioList = m_ctrlContainer->GetIOControlList();
+    if(ioList.size() != 2) {
+        fail = true;
+        failMessage = _("The control system must have one input and one output.");
+    }
+    bool haveInput, haveOutput;
+    haveInput = haveOutput = false;
+    for(auto it = ioList.begin(), itEnd = ioList.end(); it != itEnd; ++it) {
+        IOControl* io = *it;
+        if(io->GetType() == Node::NODE_OUT) {
+            m_inputControl = io;
+            haveInput = true;
+        } else if(io->GetType() == Node::NODE_IN) {
+            m_outputControl = io;
+            haveOutput = true;
+        }
+    }
+    if(!fail && !haveInput) {
+        fail = true;
+        failMessage = _("There is no input in the control system.");
+    }
+    if(!fail && !haveOutput) {
+        fail = true;
+        failMessage = _("There is no output in the control system.");
+    }
+    if(!fail) {
+        if(m_inputControl->GetChildList().size() == 0) {
+            fail = true;
+            failMessage = _("Input not connected.");
+        }
+    }
+
+    m_timeStep = timeStep;
+    m_integrationError = integrationError;
+    if(!fail) {
+        if(!InitializeValues(input, startAllZero)) {
+            fail = true;
+            failMessage = _("It was not possible to initialize the control system.");
+        }
+    }
+
+    if(fail) {
+        wxMessageDialog msgDialog(controlEditor, failMessage, _("Error"), wxOK | wxCENTRE | wxICON_ERROR);
+        msgDialog.ShowModal();
+    } else {
+        m_isOK = true;
+    }
+}
+
+bool ControlElementSolver::InitializeValues(double input, bool startAllZero)
+{
+    // Reset Elements values
+    auto elementList = m_ctrlContainer->GetControlElementsList();
+    for(auto it = elementList.begin(), itEnd = elementList.end(); it != itEnd; ++it) {
+        ControlElement* element = *it;
+        element->SetSolved(false);
+        element->SetOutput(0.0);
+    }
+    auto tfList = m_ctrlContainer->GetTFList();
+    for(auto it = tfList.begin(), itEnd = tfList.end(); it != itEnd; ++it) {
+        TransferFunction* tf = *it;
+        tf->CalculateSpaceState(100, m_integrationError);
+    }
+    auto connectionLineList = m_ctrlContainer->GetConnectionLineList();
+    for(auto it = connectionLineList.begin(), itEnd = connectionLineList.end(); it != itEnd; ++it) {
+        ConnectionLine* cLine = *it;
+        cLine->SetSolved(false);
+        cLine->SetValue(0.0);
+    }
+
+    if(!startAllZero) {
+        double origTimeStep = m_timeStep;
+        double minStep = m_timeStep / 10;
+        double maxStep = m_timeStep * 10;
+        // Calculate the steady-state results according to the input.
+        double minError = 1e-7 * m_timeStep;
+        int maxIteration = 100 / m_timeStep;
+
+        double prevSol = 0.0;
+        double currentSol = 1.0;
+        double error = 1.0;
+        double prevError = 1.0;
+        int numIt = 0;
+        while(error > minError) {
+            prevSol = currentSol;
+            prevError = error;
+            SolveNextStep(input);
+            currentSol = GetLastSolution();
+            numIt++;
+            error = std::abs(prevSol - currentSol);
+            if(std::abs(error - prevError) < 1e-1) {
+                if(m_timeStep < maxStep) {
+                    m_timeStep *= 1.5;
+                }
+            } else if(std::abs(error - prevError) > 10) {
+                if(m_timeStep > minStep) {
+                    m_timeStep /= 1.5;
+                }
+            }
+            if(numIt >= maxIteration) return false;
+        }
+        m_timeStep = origTimeStep;
+        m_solutions.clear();
+    }
+
+    return true;
+}
+
+void ControlElementSolver::SolveNextStep(double input)
+{
+    // Set all elements as not solved
+    auto elementList = m_ctrlContainer->GetControlElementsList();
+    for(auto it = elementList.begin(), itEnd = elementList.end(); it != itEnd; ++it) {
+        ControlElement* element = *it;
+        element->SetSolved(false);
+    }
+    auto connectionLineList = m_ctrlContainer->GetConnectionLineList();
+    for(auto it = connectionLineList.begin(), itEnd = connectionLineList.end(); it != itEnd; ++it) {
+        ConnectionLine* cLine = *it;
+        cLine->SetSolved(false);
+    }
+
+    // Get first node and set input value on connected lines
+    ConnectionLine* firstConn = static_cast<ConnectionLine*>(m_inputControl->GetChildList()[0]);
+    m_inputControl->SetSolved();
+    firstConn->SetValue(input);
+    firstConn->SetSolved();
+    FillAllConnectedChildren(firstConn);
+
+    // Set value to the connected lines in constants
+    auto constantList = m_ctrlContainer->GetConstantList();
+    for(auto it = constantList.begin(), itEnd = constantList.end(); it != itEnd; ++it) {
+        Constant* constant = *it;
+        if(constant->GetChildList().size() == 1) {
+            constant->SetSolved();
+            ConnectionLine* child = static_cast<ConnectionLine*>(constant->GetChildList()[0]);
+            child->SetValue(constant->GetValue());
+            child->SetSolved();
+            FillAllConnectedChildren(child);
+        }
+    }
+
+    ConnectionLine* currentLine = firstConn;
+    while(currentLine) {
+        currentLine = SolveNextElement(currentLine);
+    }
+
+    bool haveUnsolvedElement = true;
+    while(haveUnsolvedElement) {
+        haveUnsolvedElement = false;
+        // Get the solved line connected with unsolved element (elements not connected in the main branch).
+        for(auto it = connectionLineList.begin(), itEnd = connectionLineList.end(); it != itEnd; ++it) {
+            ConnectionLine* cLine = *it;
+            if(cLine->IsSolved()) {
+                auto parentList = cLine->GetParentList();
+                for(auto itP = parentList.begin(), itPEnd = parentList.end(); itP != itPEnd; ++itP) {
+                    ControlElement* parent = static_cast<ControlElement*>(*itP);
+                    if(!parent->IsSolved()) {
+                        haveUnsolvedElement = true;
+                        // Solve secondary branch.
+                        currentLine = cLine;
+                        while(currentLine) {
+                            currentLine = SolveNextElement(currentLine);
+                        }
+                        break;
+                    }
+                }
+            }
+            if(haveUnsolvedElement) break;
+        }
+    }
+
+    // Set the control system step output.
+    if(m_outputControl->GetChildList().size() == 1) {
+        ConnectionLine* cLine = static_cast<ConnectionLine*>(m_outputControl->GetChildList()[0]);
+        m_solutions.push_back(cLine->GetValue());
+    } else
+        m_solutions.push_back(0.0);
+}
+
+void ControlElementSolver::FillAllConnectedChildren(ConnectionLine* parent)
+{
+    auto childList = parent->GetLineChildList();
+    for(auto it = childList.begin(), itEnd = childList.end(); it != itEnd; ++it) {
+        ConnectionLine* child = *it;
+        child->SetValue(parent->GetValue());
+        child->SetSolved();
+        FillAllConnectedChildren(child);
+    }
+}
+
+ConnectionLine* ControlElementSolver::SolveNextElement(ConnectionLine* currentLine)
+{
+    auto parentList = currentLine->GetParentList();
+    for(auto it = parentList.begin(), itEnd = parentList.end(); it != itEnd; ++it) {
+        ControlElement* element = static_cast<ControlElement*>(*it);
+        // Solve the unsolved parent.
+        if(!element->IsSolved()) {
+            if(!element->Solve(currentLine->GetValue(), m_timeStep)) return NULL;
+            element->SetSolved();
+
+            // Get the output node (must have one or will result NULL).
+            Node* outNode = NULL;
+            auto nodeList = element->GetNodeList();
+            for(auto itN = nodeList.begin(), itNEnd = nodeList.end(); itN != itNEnd; ++itN) {
+                Node* node = *itN;
+                if(node->GetNodeType() == Node::NODE_OUT) outNode = node;
+            }
+            if(!outNode) return NULL;
+
+            // Set connection line value associated with the output node.
+            auto childList = element->GetChildList();
+            for(auto itC = childList.begin(), itCEnd = childList.end(); itC != itCEnd; ++itC) {
+                ConnectionLine* cLine = static_cast<ConnectionLine*>(*itC);
+                if(!cLine->IsSolved()) {  // Only check unsolved lines
+                    // Check if the connection line have the output node on the list
+                    auto lineNodeList = cLine->GetNodeList();
+                    for(auto itCN = nodeList.begin(), itCNEnd = nodeList.end(); itCN != itCNEnd; ++itCN) {
+                        Node* childNode = *itCN;
+                        if(childNode == outNode) {
+                            // Check if the line connect two elements, otherwise return NULL
+                            if(cLine->GetType() != ConnectionLine::ELEMENT_ELEMENT) return NULL;
+
+                            // Set the connection line value and return it.
+                            cLine->SetValue(element->GetOutput());
+                            cLine->SetSolved();
+                            FillAllConnectedChildren(cLine);
+                            return cLine;
+                        }
+                    }
+                }
+            }
+        }
+    }
+    return NULL;
+}
diff --git a/Project/ControlElementSolver.h b/Project/ControlElementSolver.h
new file mode 100644
index 0000000..6d0ad3f
--- /dev/null
+++ b/Project/ControlElementSolver.h
@@ -0,0 +1,49 @@
+#ifndef CONTROLELEMENTSOLVER_H
+#define CONTROLELEMENTSOLVER_H
+
+#include <stddef.h>  // NULL definition
+#include <vector>
+
+class ControlElementContainer;
+class ControlEditor;
+class ConnectionLine;
+class Constant;
+class Exponential;
+class Gain;
+class IOControl;
+class Limiter;
+class Multiplier;
+class RateLimiter;
+class Sum;
+class TransferFunction;
+
+class ControlElementSolver
+{
+   public:
+    ControlElementSolver() {}
+    ControlElementSolver(ControlEditor* controlEditor,
+                         double timeStep = 1e-3,
+                         double integrationError = 1e-3,
+                         bool startAllZero = false,
+                         double input = 0.0);
+    ~ControlElementSolver() {}
+    virtual bool InitializeValues(double input, bool startAllZero);
+    virtual void SolveNextStep(double input);
+    virtual std::vector<double> GetSolutions() { return m_solutions; }
+    virtual double GetLastSolution() { return m_solutions[m_solutions.size() - 1]; }
+    virtual bool IsOK() const { return m_isOK; }
+   protected:
+    void FillAllConnectedChildren(ConnectionLine* parent);
+    ConnectionLine* SolveNextElement(ConnectionLine* currentLine);
+
+    ControlElementContainer* m_ctrlContainer = NULL;
+    double m_timeStep;
+    double m_integrationError;
+    std::vector<double> m_solutions;
+    bool m_isOK = false;
+
+    IOControl* m_inputControl = NULL;
+    IOControl* m_outputControl = NULL;
+};
+
+#endif  // CONTROLELEMENTSOLVER_H
diff --git a/Project/Exponential.cpp b/Project/Exponential.cpp
index 7c4f1fe..e0daeef 100644
--- a/Project/Exponential.cpp
+++ b/Project/Exponential.cpp
@@ -111,3 +111,9 @@ void Exponential::SetValues(double aValue, double bValue)
     m_aValue = aValue;
     m_bValue = bValue;
 }
+
+bool Exponential::Solve(double input, double timeStep)
+{
+    m_output = m_aValue * std::exp(m_bValue * input);
+    return true;
+}
diff --git a/Project/Exponential.h b/Project/Exponential.h
index 8260d66..e9e9511 100644
--- a/Project/Exponential.h
+++ b/Project/Exponential.h
@@ -22,6 +22,8 @@ public:
     virtual void GetValues(double& aValue, double &bValue);
     virtual void SetValues(double aValue, double bValue);
     
+    virtual bool Solve(double input, double timeStep);
+    
 protected:
     double m_aValue = 0.001;
     double m_bValue = 5.0;
diff --git a/Project/Gain.cpp b/Project/Gain.cpp
index faea89c..d2106d7 100644
--- a/Project/Gain.cpp
+++ b/Project/Gain.cpp
@@ -167,3 +167,9 @@ void Gain::Move(wxPoint2DDouble position)
     SetPosition(m_movePos + position - m_moveStartPt);
     UpdatePoints();
 }
+
+bool Gain::Solve(double input, double timeStep)
+{
+    m_output = input * m_value;
+    return true;
+}
diff --git a/Project/Gain.h b/Project/Gain.h
index 8844372..bb9c3ce 100644
--- a/Project/Gain.h
+++ b/Project/Gain.h
@@ -24,6 +24,8 @@ class Gain : public ControlElement
     virtual void SetValue(double value);
     virtual double GetValue() const { return m_value; }
     virtual void UpdatePoints();
+    
+    virtual bool Solve(double input, double timeStep);
 
    protected:
     double m_value = 1.0;
diff --git a/Project/IOControl.h b/Project/IOControl.h
index 7b3f4d0..8a7666f 100644
--- a/Project/IOControl.h
+++ b/Project/IOControl.h
@@ -35,6 +35,7 @@ class IOControl : public ControlElement
     virtual IOFlags GetValue() const { return m_value; }
     virtual void SetValue(IOFlags value);
     virtual int GetIOFlags() const { return m_ioFlags; }
+    virtual Node::NodeType GetType() { return m_ioNodeType; }
 
    protected:
     IOFlags m_value;
diff --git a/Project/Limiter.cpp b/Project/Limiter.cpp
index 2a0b707..cd76fba 100644
--- a/Project/Limiter.cpp
+++ b/Project/Limiter.cpp
@@ -87,3 +87,12 @@ void Limiter::UpdatePoints()
         m_nodeList[1]->SetPosition(m_position + wxPoint2DDouble(0, -18));
     }
 }
+
+bool Limiter::Solve(double input, double timeStep)
+{
+    m_output = input;
+    if(m_output > m_upLimit) m_output = m_upLimit;
+    else if(m_output < m_lowLimit) m_output = m_lowLimit;
+    
+    return true;
+}
diff --git a/Project/Limiter.h b/Project/Limiter.h
index 5f4e55b..1585a3c 100644
--- a/Project/Limiter.h
+++ b/Project/Limiter.h
@@ -16,6 +16,7 @@ public:
     virtual bool Intersects(wxRect2DDouble rect) const { return m_rect.Intersects(rect); }
     virtual bool ShowForm(wxWindow* parent, Element* element);
     virtual void Rotate(bool clockwise = true);
+    virtual bool Solve(double input, double timeStep);
 
     virtual void UpdatePoints();
     
diff --git a/Project/Multiplier.cpp b/Project/Multiplier.cpp
index ee644ed..e8708c9 100644
--- a/Project/Multiplier.cpp
+++ b/Project/Multiplier.cpp
@@ -1,12 +1,12 @@
 #include "Multiplier.h"
+#include "ConnectionLine.h"
 
 Multiplier::Multiplier(int id) : ControlElement(id)
 {
     m_width = m_height = 36.0;
     Node* nodeIn1 = new Node(m_position + wxPoint2DDouble(-18, -9), Node::NODE_IN, m_borderSize);
     nodeIn1->StartMove(m_position);
-    Node* nodeIn2 =
-        new Node(m_position + wxPoint2DDouble(-18, 9), Node::NODE_IN, m_borderSize);
+    Node* nodeIn2 = new Node(m_position + wxPoint2DDouble(-18, 9), Node::NODE_IN, m_borderSize);
     nodeIn2->StartMove(m_position);
     Node* nodeOut = new Node(m_position + wxPoint2DDouble(18, 0), Node::NODE_OUT, m_borderSize);
     nodeOut->SetAngle(180.0);
@@ -17,7 +17,6 @@ Multiplier::Multiplier(int id) : ControlElement(id)
 }
 
 Multiplier::~Multiplier() {}
-
 void Multiplier::Draw(wxPoint2DDouble translation, double scale) const
 {
     glLineWidth(1.0);
@@ -30,7 +29,7 @@ void Multiplier::Draw(wxPoint2DDouble translation, double scale) const
     DrawRectangle(m_position, m_width, m_height);
     glColor4d(0.0, 0.0, 0.0, 1.0);
     DrawRectangle(m_position, m_width, m_height, GL_LINE_LOOP);
-    
+
     // Plot x.
     glLineWidth(2.0);
     std::vector<wxPoint2DDouble> xSymbol;
@@ -84,3 +83,35 @@ void Multiplier::UpdatePoints()
         m_nodeList[2]->SetPosition(m_position + wxPoint2DDouble(0, -18));
     }
 }
+
+bool Multiplier::Solve(double input, double timeStep)
+{
+    std::vector<double> inputVector;
+    for(auto itN = m_nodeList.begin(), itNEnd = m_nodeList.end(); itN != itNEnd; ++itN) {
+        Node* node = *itN;
+        if(node->GetNodeType() != Node::NODE_OUT) {
+            if(!node->IsConnected()) {
+                inputVector.push_back(1.0);
+            } else {
+                for(auto itC = m_childList.begin(), itCEnd = m_childList.end(); itC != itCEnd; ++itC) {
+                    ConnectionLine* cLine = static_cast<ConnectionLine*>(*itC);
+                    auto nodeList = cLine->GetNodeList();
+                    for(auto itCN = nodeList.begin(), itCNEnd = nodeList.end(); itCN != itCNEnd; ++itCN) {
+                        Node* childNode = *itCN;
+                        if(childNode == node) {
+                            inputVector.push_back(cLine->GetValue());
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    m_output = 1.0;
+    for(unsigned int i = 0; i < inputVector.size(); ++i) {
+        m_output *= inputVector[i];
+    }
+
+    return true;
+}
diff --git a/Project/Multiplier.h b/Project/Multiplier.h
index 8a25b23..19fca71 100644
--- a/Project/Multiplier.h
+++ b/Project/Multiplier.h
@@ -3,6 +3,8 @@
 
 #include "ControlElement.h"
 
+class ConnectionLine;
+
 class Multiplier : public ControlElement
 {
    public:
@@ -16,6 +18,8 @@ class Multiplier : public ControlElement
     virtual void Rotate(bool clockwise = true);
 
     virtual void UpdatePoints();
+    
+    virtual bool Solve(double input, double timeStep);
 };
 
 #endif  // MULTIPLIER_H
diff --git a/Project/Project.mk b/Project/Project.mk
index c43d7d9..b9d2fb9 100644
--- a/Project/Project.mk
+++ b/Project/Project.mk
@@ -13,7 +13,7 @@ CurrentFileName        :=
 CurrentFilePath        :=
 CurrentFileFullPath    :=
 User                   :=NDSE-69
-Date                   :=03/05/2017
+Date                   :=13/05/2017
 CodeLitePath           :="C:/Program Files/CodeLite"
 LinkerName             :=C:/TDM-GCC-64/bin/g++.exe
 SharedObjectLinkerName :=C:/TDM-GCC-64/bin/g++.exe -shared -fPIC
@@ -69,9 +69,9 @@ Objects0=$(IntermediateDirectory)/main.cpp$(ObjectSuffix) $(IntermediateDirector
 	$(IntermediateDirectory)/WorkspaceBase.cpp$(ObjectSuffix) $(IntermediateDirectory)/ElementForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/ControlEditorBase.cpp$(ObjectSuffix) $(IntermediateDirectory)/ChartViewBase.cpp$(ObjectSuffix) $(IntermediateDirectory)/Bus.cpp$(ObjectSuffix) $(IntermediateDirectory)/Line.cpp$(ObjectSuffix) $(IntermediateDirectory)/Transformer.cpp$(ObjectSuffix) $(IntermediateDirectory)/Machines.cpp$(ObjectSuffix) $(IntermediateDirectory)/SyncGenerator.cpp$(ObjectSuffix) $(IntermediateDirectory)/IndMotor.cpp$(ObjectSuffix) \
 	$(IntermediateDirectory)/Branch.cpp$(ObjectSuffix) $(IntermediateDirectory)/SyncMotor.cpp$(ObjectSuffix) $(IntermediateDirectory)/Shunt.cpp$(ObjectSuffix) $(IntermediateDirectory)/Load.cpp$(ObjectSuffix) $(IntermediateDirectory)/Inductor.cpp$(ObjectSuffix) $(IntermediateDirectory)/Capacitor.cpp$(ObjectSuffix) $(IntermediateDirectory)/PowerElement.cpp$(ObjectSuffix) $(IntermediateDirectory)/ElectricCalculation.cpp$(ObjectSuffix) $(IntermediateDirectory)/PowerFlow.cpp$(ObjectSuffix) $(IntermediateDirectory)/Fault.cpp$(ObjectSuffix) \
 	$(IntermediateDirectory)/Text.cpp$(ObjectSuffix) $(IntermediateDirectory)/GraphicalElement.cpp$(ObjectSuffix) $(IntermediateDirectory)/ControlElement.cpp$(ObjectSuffix) $(IntermediateDirectory)/TransferFunction.cpp$(ObjectSuffix) $(IntermediateDirectory)/ConnectionLine.cpp$(ObjectSuffix) $(IntermediateDirectory)/Sum.cpp$(ObjectSuffix) $(IntermediateDirectory)/Multiplier.cpp$(ObjectSuffix) $(IntermediateDirectory)/Limiter.cpp$(ObjectSuffix) $(IntermediateDirectory)/RateLimiter.cpp$(ObjectSuffix) $(IntermediateDirectory)/Exponential.cpp$(ObjectSuffix) \
-	$(IntermediateDirectory)/Constant.cpp$(ObjectSuffix) $(IntermediateDirectory)/Gain.cpp$(ObjectSuffix) $(IntermediateDirectory)/IOControl.cpp$(ObjectSuffix) $(IntermediateDirectory)/ControlElementContainer.cpp$(ObjectSuffix) $(IntermediateDirectory)/wxMathPlot_mathplot.cpp$(ObjectSuffix) $(IntermediateDirectory)/BusForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/GeneratorStabForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/LineForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/SwitchingForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/TransformerForm.cpp$(ObjectSuffix) \
-	$(IntermediateDirectory)/LoadForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/ReactiveShuntElementForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/IndMotorForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/SyncMachineForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/TextForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/TransferFunctionForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/SumForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/LimiterForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/RateLimiterForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/ExponentialForm.cpp$(ObjectSuffix) \
-	$(IntermediateDirectory)/ConstantForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/GainForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/IOControlForm.cpp$(ObjectSuffix) 
+	$(IntermediateDirectory)/Constant.cpp$(ObjectSuffix) $(IntermediateDirectory)/Gain.cpp$(ObjectSuffix) $(IntermediateDirectory)/IOControl.cpp$(ObjectSuffix) $(IntermediateDirectory)/ControlElementContainer.cpp$(ObjectSuffix) $(IntermediateDirectory)/ControlElementSolver.cpp$(ObjectSuffix) $(IntermediateDirectory)/wxMathPlot_mathplot.cpp$(ObjectSuffix) $(IntermediateDirectory)/BusForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/GeneratorStabForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/LineForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/SwitchingForm.cpp$(ObjectSuffix) \
+	$(IntermediateDirectory)/TransformerForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/LoadForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/ReactiveShuntElementForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/IndMotorForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/SyncMachineForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/TextForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/TransferFunctionForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/SumForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/LimiterForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/RateLimiterForm.cpp$(ObjectSuffix) \
+	$(IntermediateDirectory)/ExponentialForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/ConstantForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/GainForm.cpp$(ObjectSuffix) $(IntermediateDirectory)/IOControlForm.cpp$(ObjectSuffix) 
 
 
 
@@ -528,6 +528,14 @@ $(IntermediateDirectory)/ControlElementContainer.cpp$(DependSuffix): ControlElem
 $(IntermediateDirectory)/ControlElementContainer.cpp$(PreprocessSuffix): ControlElementContainer.cpp
 	$(CXX) $(CXXFLAGS) $(IncludePCH) $(IncludePath) $(PreprocessOnlySwitch) $(OutputSwitch) $(IntermediateDirectory)/ControlElementContainer.cpp$(PreprocessSuffix) ControlElementContainer.cpp
 
+$(IntermediateDirectory)/ControlElementSolver.cpp$(ObjectSuffix): ControlElementSolver.cpp $(IntermediateDirectory)/ControlElementSolver.cpp$(DependSuffix)
+	$(CXX) $(IncludePCH) $(SourceSwitch) "C:/Users/NDSE-69/Documents/GitHub/PSP/Project/ControlElementSolver.cpp" $(CXXFLAGS) $(ObjectSwitch)$(IntermediateDirectory)/ControlElementSolver.cpp$(ObjectSuffix) $(IncludePath)
+$(IntermediateDirectory)/ControlElementSolver.cpp$(DependSuffix): ControlElementSolver.cpp
+	@$(CXX) $(CXXFLAGS) $(IncludePCH) $(IncludePath) -MG -MP -MT$(IntermediateDirectory)/ControlElementSolver.cpp$(ObjectSuffix) -MF$(IntermediateDirectory)/ControlElementSolver.cpp$(DependSuffix) -MM ControlElementSolver.cpp
+
+$(IntermediateDirectory)/ControlElementSolver.cpp$(PreprocessSuffix): ControlElementSolver.cpp
+	$(CXX) $(CXXFLAGS) $(IncludePCH) $(IncludePath) $(PreprocessOnlySwitch) $(OutputSwitch) $(IntermediateDirectory)/ControlElementSolver.cpp$(PreprocessSuffix) ControlElementSolver.cpp
+
 $(IntermediateDirectory)/wxMathPlot_mathplot.cpp$(ObjectSuffix): wxMathPlot/mathplot.cpp $(IntermediateDirectory)/wxMathPlot_mathplot.cpp$(DependSuffix)
 	$(CXX) $(IncludePCH) $(SourceSwitch) "C:/Users/NDSE-69/Documents/GitHub/PSP/Project/wxMathPlot/mathplot.cpp" $(CXXFLAGS) $(ObjectSwitch)$(IntermediateDirectory)/wxMathPlot_mathplot.cpp$(ObjectSuffix) $(IncludePath)
 $(IntermediateDirectory)/wxMathPlot_mathplot.cpp$(DependSuffix): wxMathPlot/mathplot.cpp
diff --git a/Project/Project.project b/Project/Project.project
index 6671989..752ee00 100644
--- a/Project/Project.project
+++ b/Project/Project.project
@@ -49,6 +49,7 @@
         <File Name="Gain.cpp"/>
         <File Name="IOControl.cpp"/>
         <File Name="ControlElementContainer.cpp"/>
+        <File Name="ControlElementSolver.cpp"/>
       </VirtualDirectory>
       <File Name="ElementPlotData.cpp"/>
     </VirtualDirectory>
@@ -140,6 +141,7 @@
         <File Name="Gain.h"/>
         <File Name="IOControl.h"/>
         <File Name="ControlElementContainer.h"/>
+        <File Name="ControlElementSolver.h"/>
       </VirtualDirectory>
       <File Name="ElementPlotData.h"/>
     </VirtualDirectory>
diff --git a/Project/Project.txt b/Project/Project.txt
index fbf464d..65a2851 100644
--- a/Project/Project.txt
+++ b/Project/Project.txt
@@ -1 +1 @@
-./Release/main.cpp.o ./Release/win_resources.rc.o ./Release/ElementDataObject.cpp.o ./Release/Element.cpp.o ./Release/ElementPlotData.cpp.o ./Release/ArtMetro.cpp.o ./Release/wxGLString.cpp.o ./Release/MainFrame.cpp.o ./Release/Workspace.cpp.o ./Release/FileHanding.cpp.o ./Release/ControlEditor.cpp.o ./Release/Camera.cpp.o ./Release/ChartView.cpp.o ./Release/MainFrameBitmaps.cpp.o ./Release/WorkspaceBitmaps.cpp.o ./Release/BusFormBitmaps.cpp.o ./Release/ElementFormBitmaps.cpp.o ./Release/ControlEditorBitmaps.cpp.o ./Release/ChartViewBitmaps.cpp.o ./Release/MainFrameBase.cpp.o ./Release/WorkspaceBase.cpp.o ./Release/ElementForm.cpp.o ./Release/ControlEditorBase.cpp.o ./Release/ChartViewBase.cpp.o ./Release/Bus.cpp.o ./Release/Line.cpp.o ./Release/Transformer.cpp.o ./Release/Machines.cpp.o ./Release/SyncGenerator.cpp.o ./Release/IndMotor.cpp.o ./Release/Branch.cpp.o ./Release/SyncMotor.cpp.o ./Release/Shunt.cpp.o ./Release/Load.cpp.o ./Release/Inductor.cpp.o ./Release/Capacitor.cpp.o ./Release/PowerElement.cpp.o ./Release/ElectricCalculation.cpp.o ./Release/PowerFlow.cpp.o ./Release/Fault.cpp.o ./Release/Text.cpp.o ./Release/GraphicalElement.cpp.o ./Release/ControlElement.cpp.o ./Release/TransferFunction.cpp.o ./Release/ConnectionLine.cpp.o ./Release/Sum.cpp.o ./Release/Multiplier.cpp.o ./Release/Limiter.cpp.o ./Release/RateLimiter.cpp.o ./Release/Exponential.cpp.o ./Release/Constant.cpp.o ./Release/Gain.cpp.o ./Release/IOControl.cpp.o ./Release/ControlElementContainer.cpp.o ./Release/wxMathPlot_mathplot.cpp.o ./Release/BusForm.cpp.o ./Release/GeneratorStabForm.cpp.o ./Release/LineForm.cpp.o ./Release/SwitchingForm.cpp.o ./Release/TransformerForm.cpp.o ./Release/LoadForm.cpp.o ./Release/ReactiveShuntElementForm.cpp.o ./Release/IndMotorForm.cpp.o ./Release/SyncMachineForm.cpp.o ./Release/TextForm.cpp.o ./Release/TransferFunctionForm.cpp.o ./Release/SumForm.cpp.o ./Release/LimiterForm.cpp.o ./Release/RateLimiterForm.cpp.o ./Release/ExponentialForm.cpp.o ./Release/ConstantForm.cpp.o ./Release/GainForm.cpp.o ./Release/IOControlForm.cpp.o   
+./Release/main.cpp.o ./Release/win_resources.rc.o ./Release/ElementDataObject.cpp.o ./Release/Element.cpp.o ./Release/ElementPlotData.cpp.o ./Release/ArtMetro.cpp.o ./Release/wxGLString.cpp.o ./Release/MainFrame.cpp.o ./Release/Workspace.cpp.o ./Release/FileHanding.cpp.o ./Release/ControlEditor.cpp.o ./Release/Camera.cpp.o ./Release/ChartView.cpp.o ./Release/MainFrameBitmaps.cpp.o ./Release/WorkspaceBitmaps.cpp.o ./Release/BusFormBitmaps.cpp.o ./Release/ElementFormBitmaps.cpp.o ./Release/ControlEditorBitmaps.cpp.o ./Release/ChartViewBitmaps.cpp.o ./Release/MainFrameBase.cpp.o ./Release/WorkspaceBase.cpp.o ./Release/ElementForm.cpp.o ./Release/ControlEditorBase.cpp.o ./Release/ChartViewBase.cpp.o ./Release/Bus.cpp.o ./Release/Line.cpp.o ./Release/Transformer.cpp.o ./Release/Machines.cpp.o ./Release/SyncGenerator.cpp.o ./Release/IndMotor.cpp.o ./Release/Branch.cpp.o ./Release/SyncMotor.cpp.o ./Release/Shunt.cpp.o ./Release/Load.cpp.o ./Release/Inductor.cpp.o ./Release/Capacitor.cpp.o ./Release/PowerElement.cpp.o ./Release/ElectricCalculation.cpp.o ./Release/PowerFlow.cpp.o ./Release/Fault.cpp.o ./Release/Text.cpp.o ./Release/GraphicalElement.cpp.o ./Release/ControlElement.cpp.o ./Release/TransferFunction.cpp.o ./Release/ConnectionLine.cpp.o ./Release/Sum.cpp.o ./Release/Multiplier.cpp.o ./Release/Limiter.cpp.o ./Release/RateLimiter.cpp.o ./Release/Exponential.cpp.o ./Release/Constant.cpp.o ./Release/Gain.cpp.o ./Release/IOControl.cpp.o ./Release/ControlElementContainer.cpp.o ./Release/ControlElementSolver.cpp.o ./Release/wxMathPlot_mathplot.cpp.o ./Release/BusForm.cpp.o ./Release/GeneratorStabForm.cpp.o ./Release/LineForm.cpp.o ./Release/SwitchingForm.cpp.o ./Release/TransformerForm.cpp.o ./Release/LoadForm.cpp.o ./Release/ReactiveShuntElementForm.cpp.o ./Release/IndMotorForm.cpp.o ./Release/SyncMachineForm.cpp.o ./Release/TextForm.cpp.o ./Release/TransferFunctionForm.cpp.o ./Release/SumForm.cpp.o ./Release/LimiterForm.cpp.o ./Release/RateLimiterForm.cpp.o ./Release/ExponentialForm.cpp.o ./Release/ConstantForm.cpp.o ./Release/GainForm.cpp.o ./Release/IOControlForm.cpp.o   
diff --git a/Project/RateLimiter.cpp b/Project/RateLimiter.cpp
index 5da0578..42bede1 100644
--- a/Project/RateLimiter.cpp
+++ b/Project/RateLimiter.cpp
@@ -13,10 +13,7 @@ RateLimiter::RateLimiter(int id) : ControlElement(id)
     m_nodeList.push_back(nodeOut);
 }
 
-RateLimiter::~RateLimiter()
-{
-}
-
+RateLimiter::~RateLimiter() {}
 void RateLimiter::Draw(wxPoint2DDouble translation, double scale) const
 {
     glLineWidth(1.0);
@@ -37,7 +34,7 @@ void RateLimiter::Draw(wxPoint2DDouble translation, double scale) const
     axis.push_back(m_position + wxPoint2DDouble(0, -13));
     axis.push_back(m_position + wxPoint2DDouble(0, 13));
     DrawLine(axis, GL_LINES);
-    
+
     glLineWidth(2.0);
     std::vector<wxPoint2DDouble> limSymbol;
     limSymbol.push_back(m_position + wxPoint2DDouble(10, -10));
@@ -95,3 +92,23 @@ void RateLimiter::UpdatePoints()
         m_nodeList[1]->SetPosition(m_position + wxPoint2DDouble(0, -18));
     }
 }
+
+bool RateLimiter::Solve(double input, double timeStep)
+{
+    double rate = (input - m_output) / timeStep;
+
+    bool reachLimit = false;
+    if(rate > m_upLimit) {
+        rate = m_upLimit;
+        reachLimit = true;
+    } else if(rate < m_lowLimit) {
+        rate = m_lowLimit;
+        reachLimit = true;
+    }
+
+    if(reachLimit)
+        m_output += rate * timeStep;
+    else
+        m_output = input;
+    return true;
+}
diff --git a/Project/RateLimiter.h b/Project/RateLimiter.h
index d17642b..b1e669c 100644
--- a/Project/RateLimiter.h
+++ b/Project/RateLimiter.h
@@ -24,6 +24,8 @@ class RateLimiter : public ControlElement
     void SetUpLimit(double upLimit) { m_upLimit = upLimit; }
     void SetLowLimit(double lowLimit) { m_lowLimit = lowLimit; }
     
+    virtual bool Solve(double input, double timeStep);
+    
    protected:
     double m_upLimit = 5.0;
     double m_lowLimit = -5.0;
diff --git a/Project/Sum.cpp b/Project/Sum.cpp
index 606b367..b7a4f8a 100644
--- a/Project/Sum.cpp
+++ b/Project/Sum.cpp
@@ -1,8 +1,8 @@
 #include "Sum.h"
 #include "SumForm.h"
+#include "ConnectionLine.h"
 
-Sum::Sum(int id)
-    : ControlElement(id)
+Sum::Sum(int id) : ControlElement(id)
 {
     m_width = m_height = 36.0;
     Node* nodeIn1 = new Node(m_position + wxPoint2DDouble(-m_width / 2, 9 - m_height / 2), Node::NODE_IN, m_borderSize);
@@ -23,7 +23,6 @@ Sum::Sum(int id)
 }
 
 Sum::~Sum() {}
-
 void Sum::Draw(wxPoint2DDouble translation, double scale) const
 {
     glLineWidth(1.0);
@@ -133,12 +132,13 @@ void Sum::UpdatePoints()
     else if(m_angle == 270.0)
         m_nodeList[m_nodeList.size() - 1]->SetPosition(m_position + wxPoint2DDouble(0, -m_height / 2));
 
-    SetPosition(m_position); // Update rect.
+    SetPosition(m_position);  // Update rect.
 }
 
 void Sum::AddInNode()
 {
     Node* newNode = new Node(wxPoint2DDouble(0, 0), Node::NODE_IN, m_borderSize);
+    newNode->SetAngle(m_angle);
     m_nodeList.insert(m_nodeList.end() - 1, newNode);
 }
 
@@ -181,3 +181,39 @@ void Sum::Rotate(bool clockwise)
         node->Rotate(clockwise);
     }
 }
+
+bool Sum::Solve(double input, double timeStep)
+{
+    std::vector<double> inputVector;
+    for(auto itN = m_nodeList.begin(), itNEnd = m_nodeList.end(); itN != itNEnd; ++itN) {
+        Node* node = *itN;
+        if(node->GetNodeType() != Node::NODE_OUT) {
+            if(!node->IsConnected()) {
+                inputVector.push_back(0.0);
+            } else {
+                for(auto itC = m_childList.begin(), itCEnd = m_childList.end(); itC != itCEnd; ++itC) {
+                    ConnectionLine* cLine = static_cast<ConnectionLine*>(*itC);
+                    auto nodeList = cLine->GetNodeList();
+                    for(auto itCN = nodeList.begin(), itCNEnd = nodeList.end(); itCN != itCNEnd; ++itCN) {
+                        Node* childNode = *itCN;
+                        if(childNode == node) {
+                            inputVector.push_back(cLine->GetValue());
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    if(m_signalList.size() != inputVector.size()) return false;
+
+    m_output = 0.0;
+    for(unsigned int i = 0; i < m_signalList.size(); ++i) {
+        if(m_signalList[i] == SIGNAL_POSITIVE)
+            m_output += inputVector[i];
+        else if(m_signalList[i] == SIGNAL_NEGATIVE)
+            m_output -= inputVector[i];
+    }
+    return true;
+}
diff --git a/Project/Sum.h b/Project/Sum.h
index a99067e..f3ab4c6 100644
--- a/Project/Sum.h
+++ b/Project/Sum.h
@@ -4,6 +4,7 @@
 #include "ControlElement.h"
 
 class SumForm;
+class ConnectionLine;
 
 class Sum : public ControlElement
 {
@@ -21,6 +22,8 @@ public:
     virtual std::vector<Signal> GetSignalList() const { return m_signalList; }
     virtual void SetSignalList(std::vector<Signal> signalList) { m_signalList = signalList; }
     
+    virtual bool Solve(double input, double timeStep);
+    
     virtual void UpdatePoints();
     void AddInNode();
     void RemoveInNode();
diff --git a/Project/TransferFunction.cpp b/Project/TransferFunction.cpp
index 9c8ffea..ebb59fb 100644
--- a/Project/TransferFunction.cpp
+++ b/Project/TransferFunction.cpp
@@ -32,7 +32,6 @@ TransferFunction::TransferFunction(int id) : ControlElement(id)
 }
 
 TransferFunction::~TransferFunction() {}
-
 void TransferFunction::Draw(wxPoint2DDouble translation, double scale) const
 {
     glLineWidth(1.0);
@@ -88,7 +87,7 @@ void TransferFunction::SetText(wxString numerator, wxString denominator)
 
     m_width = nWidth > dWidth ? nWidth : dWidth;
     m_height = m_glStringNum->getheight() + m_glStringDen->getheight() + 2 * m_borderSize;
-    SetPosition(m_position); // Update rect properly.
+    SetPosition(m_position);  // Update rect properly.
 }
 
 wxString TransferFunction::GetSuperscriptNumber(int number)
@@ -248,3 +247,111 @@ void TransferFunction::Rotate(bool clockwise)
         node->Rotate(clockwise);
     }
 }
+
+void TransferFunction::CalculateSpaceState(int maxIteration, double error)
+{
+    m_maxIteration = maxIteration;
+    m_error = error;
+
+    int order = static_cast<int>(m_denominator.size());
+    std::vector<double> denominator = m_denominator;
+    std::vector<double> numerator;
+
+    int k = order;
+    for(int i = 0; i < order; i++) {
+        int numIndex = i - (order - static_cast<int>(m_numerator.size()));
+        if(numIndex < 0)
+            numerator.push_back(0.0);
+        else
+            numerator.push_back(m_numerator[numIndex]);
+        k--;
+    }
+
+    SpaceState ss;
+    for(int i = 0; i < (order - 1); i++) {
+        std::vector<double> lineA;
+        for(int j = 0; j < (order - 1); j++) {
+            if(j == i + 1)
+                lineA.push_back(1.0);
+            else
+                lineA.push_back(0.0);
+        }
+        ss.A.push_back(lineA);
+        ss.B.push_back(0.0);
+        ss.C.push_back(0.0);
+    }
+    for(int i = 0; i < order - 1; i++) {
+        ss.A[order - 2][i] = -(denominator[order - 1 - i] / denominator[0]);
+        ss.C[i] = (numerator[order - 1 - i] - denominator[order - 1 - i] * numerator[0]) / denominator[0];
+    }
+    ss.B[order - 2] = 1.0;
+    ss.D = numerator[0];
+
+    m_ss = ss;
+
+    // Reset state
+    m_x.clear();
+    m_dx.clear();
+
+    for(unsigned int i = 0; i < m_denominator.size(); ++i) {
+        m_x.push_back(0.0);
+        m_dx.push_back(0.0);
+    }
+}
+
+bool TransferFunction::Solve(double input, double timeStep)
+{
+    int order = static_cast<int>(m_ss.A.size());
+
+    std::vector<double> x;
+    std::vector<double> oldx;
+    std::vector<double> dx;
+    std::vector<double> olddx;
+    for(int i = 0; i < order; i++) {
+        x.push_back(m_x[i]);
+        oldx.push_back(m_x[i]);
+
+        dx.push_back(m_dx[i]);
+        olddx.push_back(m_dx[i]);
+    }
+
+    bool exit = false;
+    int iter = 0;
+    while(!exit) {
+        double xError = 0.0;
+        double dxError = 0.0;
+        for(int i = 0; i < order; i++) {
+            // Trapezoidal method
+            x[i] = m_x[i] + 0.5 * timeStep * (m_dx[i] + dx[i]);
+
+            if(std::abs(x[i] - oldx[i]) > xError) xError = std::abs(x[i] - oldx[i]);
+
+            oldx[i] = x[i];
+        }
+        for(int i = 0; i < order; i++) {
+            // x' = Ax + Bu
+            dx[i] = 0.0;
+            for(int j = 0; j < order; j++) dx[i] += m_ss.A[i][j] * x[j];
+            dx[i] += m_ss.B[i] * input;
+
+            if(std::abs(dx[i] - olddx[i]) > dxError) dxError = std::abs(dx[i] - olddx[i]);
+
+            olddx[i] = dx[i];
+        }
+        if(std::max(xError, dxError) < m_error) exit = true;
+
+        iter++;
+        if(iter >= m_maxIteration) return false;
+    }
+
+    m_output = 0.0;
+    for(int i = 0; i < order; i++) {
+        m_output += m_ss.C[i] * x[i];
+        m_x[i] = x[i];
+        m_dx[i] = dx[i];
+    }
+
+    m_output += m_ss.D * input;
+
+    return true;
+}
diff --git a/Project/TransferFunction.h b/Project/TransferFunction.h
index 45681ce..19bd04e 100644
--- a/Project/TransferFunction.h
+++ b/Project/TransferFunction.h
@@ -10,7 +10,14 @@ class TransferFunctionForm;
 
 class TransferFunction : public ControlElement
 {
-public:
+   public:
+    struct SpaceState {
+        std::vector<std::vector<double> > A;
+        std::vector<double> B;
+        std::vector<double> C;
+        double D;
+    };
+
     TransferFunction(int id);
     ~TransferFunction();
 
@@ -19,25 +26,35 @@ public:
     virtual bool Intersects(wxRect2DDouble rect) const { return m_rect.Intersects(rect); }
     virtual bool ShowForm(wxWindow* parent, Element* element);
     virtual void Rotate(bool clockwise = true);
-    
+
     virtual std::vector<double> GetNumerator() const { return m_numerator; }
     virtual std::vector<double> GetDenominator() const { return m_denominator; }
     virtual void SetNumerator(std::vector<double> numerator) { m_numerator = numerator; }
     virtual void SetDenominator(std::vector<double> denominator) { m_denominator = denominator; }
     virtual void UpdateTFText();
-    
-protected:
+    virtual SpaceState GetSpaceState() { return m_ss; }
+    virtual void CalculateSpaceState(int maxIteration = 100, double error = 1e-3);
+    virtual bool Solve(double input, double timeStep);
+
+   protected:
     virtual void SetText(wxString numerator, wxString denominator);
     virtual wxString GetSuperscriptNumber(int number);
     virtual void GetTFString(wxString& numerator, wxString& denominator);
-    
+
     wchar_t m_supNumber[10];
-    
+
     wxGLString* m_glStringNum = NULL;
     wxGLString* m_glStringDen = NULL;
     int m_fontSize = 10;
+
     std::vector<double> m_numerator;
     std::vector<double> m_denominator;
+    SpaceState m_ss;
+
+    std::vector<double> m_x;
+    std::vector<double> m_dx;
+    double m_error = 1e-3;
+    int m_maxIteration = 100;
 };
 
-#endif // TRANSFERFUNCTION_H
+#endif  // TRANSFERFUNCTION_H