I’m writing a program in C# using Unity to find the optimal solution to a linear programming problem using the simplex method, for my computer science coursework. Unfortunately I’m not very experienced with C# or Unity, and I’ve run into an issue with one section of my code.
Here’s a short breakdown of linear programming for some context:(I’m only coding for one-stage linear programming with two variables)You have an objective function which you’re trying to maximise e.g. P = 3x + 2yThere are also a number of limiting constraints on the problem e.g. 2x + y <= 18 or 3x + y <= 24The most common method used to solve a problem like this is the simplex method, where all the values are stored in a table and then operated on until the optimal solutions for x and y are found (this website explains it a lot better: https://www.phpsimplex.com/en/simplex_method_example.htm#google_vignette).
In my project, the code to carry out the simplex method gets executed over a number of Unity scenes.In the first scene, the number of constraints on the problem is obtained from the user and the values in each constraint itself are stored to a matrix class 2D float array called simplexTable. The dimensions and elements of simplexTable are stored using the Player Prefs class so they can be accessed from the next scene.In the next scene, the user enters the objective function on the problem and the x and y coefficients are stored to simplexTable. Then, they click on a ‘next’ button which takes them to the next scene. In this scene, I call the method which actually carries out the simplex method and this scene is where my issue is.
Using Debug.Log statements, I’ve managed to verify that the method is called and the data in simplexMethod is successfully retrieved from Player Prefs and restored into the simplexTable array - everything works as it should up to here.
After this, I use a while loop, since I only want to continue applying the simplex method while the table is unmaximised (i.e. while an optimal solution has not been found) but whenever the code reaches this part, my Unity Editor app just freezes and I have to force quit it. I’ve done some research on this problem and apparently it can happen when your code has an infinite loop, but I’ve included a break statement which should be logically sound, and the values I’m entering while testing the program should give a solution which allows the loop to be broken out of. It could be because my laptop is quite old and only has 4GB of RAM, but I’m not sure.
I’ve pasted the part of my code that includes the while loop below.
So sorry for the bad explanation but I would really appreciate it if someone could help. Thank you so much in advance!
My Code:
bool maximised = false;//while the table is unmaximisedwhile (!maximised){Debug.Log("while loop started");
int count = 0;float[] pivotValueArr = new float[numberOfConstraints + 4];float[] pivotColumn = new float[numberOfConstraints];float pivotValueCol;//iterates through each element in the objective row to check for negative valuesfor (int ii = 0; ii < simplexTable.GetColumns(); ii++){ if (ii < simplexTable.GetColumns()) { Debug.Log($"ii: {ii}, Rows: {simplexTable.GetRows()}, Columns: {simplexTable.GetColumns()}"); if (simplexTable[0, ii] < 0)//IndexOutOfRangeException: Index was outside the bounds of the array { pivotValueArr[ii] = simplexTable[0, ii]; count++; } else { pivotValueArr[ii] = 0; } } else { Debug.LogError($"Index out of bounds: ii={ii}, Columns={simplexTable.GetColumns()}"); }}Debug.Log($"Loop execution: count = {count}, maximised = {maximised}");if (count == 0){ //maximised = true; Debug.Log("break actually gets called"); break;}pivotValueCol = pivotValueArr.Min();int pivotValueIndex = Array.IndexOf(pivotValueArr, pivotValueArr.Min());for (int i = 0; i < numberOfConstraints; i++){ pivotColumn[i] = simplexTable[i, pivotValueIndex];}float[] ratioTestArr = new float[numberOfConstraints];ratioTestArr[0] = 0;for (int i = 1; i < pivotColumn.Length; i++){ if (simplexTable[i, pivotValueIndex] > 0) { ratioTestArr[i] = simplexTable[i, numberOfConstraints + 3] / simplexTable[i, pivotValueIndex]; } }int pivotRow = Array.IndexOf(ratioTestArr, ratioTestArr.Min());float pivotCell = simplexTable[pivotRow, pivotValueIndex];for (int i = 0; i < numberOfConstraints; i++){ if (i == pivotRow) { for (int j = 0; j <= numberOfConstraints + 3; j++) { simplexTable[i, j] = simplexTable[i, j] / pivotCell; } } else { simplexTable[i, pivotValueIndex] = 0; for (int j = 0; j <= numberOfConstraints + 3; j++) { if (j != pivotValueIndex) { simplexTable[i, j] = simplexTable[i, j] - simplexTable[i, j] * (simplexTable[pivotRow, j] / pivotCell); } } }}}
I’ve tried adding Debug.Log statements to identify the error, shutting down all my other apps in case they were taking up too much memory, and checking for logic errors which would cause the loop to execute infinitely.