Lets gooooo

BusinessLogic/Algorithms/DualSimplex.cs

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+using Common;
+using Models;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BusinessLogic.Algorithms
+{
+    public class DualSimplex : Algorithm
+    {
+        public override void PutModelInCanonicalForm(Model model)
+        {
+
+            List<List<double>> tableZero = new List<List<double>>();
+
+            tableZero.Add(new List<double>());
+
+            foreach (var decVar in model.ObjectiveFunction.DecisionVariables)
+            {
+                tableZero[0].Add(decVar.Coefficient * -1);
+            }
+
+
+            for (int i = 0; i < model.Constraints.Count; i++)
+            {
+                tableZero[0].Add(0);
+                if (model.Constraints[i].InequalitySign == InequalitySign.EqualTo)
+                    tableZero[0].Add(0);
+            }
+
+            tableZero[0].Add(0);
+
+            var equalsConstraints = model.Constraints.Where(c => c.InequalitySign == InequalitySign.EqualTo).ToList();
+            if (equalsConstraints?.Count() > 0)
+            {
+                for (int i = 0; i < equalsConstraints.Count(); i++)
+                {
+                    model.Constraints[model.Constraints.FindIndex(c => c == equalsConstraints[i])].InequalitySign = InequalitySign.LessThanOrEqualTo;
+                    var newConstraint = new Constraint();
+                    newConstraint.InequalitySign = InequalitySign.GreaterThanOrEqualTo;
+                    newConstraint.RightHandSide = equalsConstraints[i].RightHandSide;
+
+                    foreach (var decVar in equalsConstraints[i].DecisionVariables)
+                    {
+                        newConstraint.DecisionVariables.Add(new DecisionVariable() { Coefficient = decVar.Coefficient });
+                    }
+
+                    model.Constraints.Add(newConstraint);
+                }
+            }
+
+            for (int i = 0; i < model.Constraints.Count; i++)
+            {
+                List<double> constraintValues = new List<double>();
+
+
+                foreach (var decVar in model.Constraints[i].DecisionVariables)
+                {
+                    if (model.Constraints[i].InequalitySign == InequalitySign.LessThanOrEqualTo)
+                    {
+                        constraintValues.Add(decVar.Coefficient);
+                    }
+                    else
+                    {
+                        constraintValues.Add(decVar.Coefficient * -1);
+                    }
+                }
+
+                for (int j = 0; j < model.Constraints.Count; j++)
+                {
+                    if (j == i)
+                    {
+                        constraintValues.Add(1);
+                    }
+                    else
+                    {
+                        constraintValues.Add(0);
+                    }
+                }
+
+                if (model.Constraints[i].InequalitySign == InequalitySign.LessThanOrEqualTo)
+                {
+                    constraintValues.Add(model.Constraints[i].RightHandSide);
+                }
+                else
+                {
+                    constraintValues.Add(model.Constraints[i].RightHandSide * -1);
+                }
+                
+                tableZero.Add(constraintValues);
+            }
+
+            model.Result.Add(tableZero);
+        }
+
+        public override void Solve(Model model)
+        {
+            Iterate(model);
+            var primalSimplex = new PrimalSimplex();
+            primalSimplex.Solve(model);
+        }
+
+        private void Iterate(Model model)
+        {
+
+            if (!CanPivot(model))
+                return;
+
+
+            int pivotRow = GetPivotRow(model);
+
+            int pivotColumn = GetPivotColumn(model, pivotRow);
+
+            if (pivotColumn == -1)
+                throw new InfeasibleException("There is no suitable column to pivot on - the problem is infeasible");
+
+            Pivot(model, pivotRow, pivotColumn);
+
+
+            Iterate(model);
+        }
+
+        private bool CanPivot(Model model)
+        {
+
+            bool canPivot = false;
+            var table = model.Result[model.Result.Count - 1];
+
+            for (int i = 1; i < table.Count; i++)
+            {
+
+                if (table[i][table[i].Count - 1] < -0.000000000001)
+                {
+                    canPivot = true;
+                    break;
+                }
+            }
+
+            return canPivot;
+        }
+
+        private int GetPivotRow(Model model)
+        {
+            int pivotRow = -1;
+            var table = model.Result[model.Result.Count - 1];
+            double mostNegative = 0;
+
+            for (int i = 1; i < table.Count; i++)
+            {
+                if (table[i][table[i].Count - 1] < 0 && table[i][table[i].Count - 1] < mostNegative)
+                {
+                    mostNegative = table[i][table[i].Count - 1];
+                    pivotRow = i;
+                }
+            }
+
+            return pivotRow;
+        }
+
+        private int GetPivotColumn(Model model, int pivotRow)
+        {
+            int pivotColumn = -1;
+            var table = model.Result[model.Result.Count - 1];
+
+            double lowestRatio = double.MaxValue;
+            for (int i = 0; i < table[0].Count - 1; i++)
+            {
+                if (table[pivotRow][i] < 0)
+                {
+                    double ratio = Math.Abs(table[0][i] / table[pivotRow][i]);
+                    if (ratio < lowestRatio)
+                    {
+                        lowestRatio = ratio;
+                        pivotColumn = i;
+                    }
+                }
+            }
+
+            return pivotColumn;
+        }
+
+        private void Pivot(Model model, int pivotRow, int pivotColumn)
+        {
+            var previousTable = model.Result[model.Result.Count - 1];
+            var newTable = new List<List<double>>();
+
+            for (int i = 0; i < previousTable.Count; i++)
+            {
+                newTable.Add(new List<double>());
+
+                for (int j = 0; j < previousTable[i].Count; j++)
+                {
+                    newTable[i].Add(previousTable[i][j]);
+                }
+            }
+
+
+            double factor = 1 / newTable[pivotRow][pivotColumn];
+            for (int i = 0; i < newTable[pivotRow].Count; i++)
+            {
+                newTable[pivotRow][i] *= factor;
+            }
+
+            double pivotColumnValue;
+            for (int i = 0; i < newTable.Count; i++)
+            {
+                pivotColumnValue = newTable[i][pivotColumn];
+
+                if (i != pivotRow && pivotColumnValue != 0)
+                {
+                    for (int j = 0; j < newTable[i].Count; j++)
+                    {
+                        newTable[i][j] += (-1 * pivotColumnValue * newTable[pivotRow][j]);
+                    }
+                }
+            }
+
+            model.Result.Add(newTable);
+        }
+    }
+}