Hi, I have to program using Fortran 90/95 simultaneous linear equations. My question is, is it possible to program this? First I did the inverse matrix to find the values of the solution of a 4X4 and 3X3 matrix. I set up [A][X] = [X]' and did the inverse matrix to find the values for [X]. So I got the solutions for x1 x2 x3 x4, ( numbers are subscripts ). Now that I know that solutions exist, can I program this with the Gauss Seidel iteration method using F 90/95? May you please explain how to set up a tolerance (say 0.000001) between two iterations because I don't understand how to since I have so many variables, or what I'm looking for? I am not asking for the specific code, just a few words to clear up how to approach this program. Thanks for your help.