Calculating linear systems using EJML

Question

How exactly do I format my code so that It would take

1x+2y+3z+4w=5e
6x+7y+8z+9w=10e
11x+12y+13z+14w=15e
16x+17y+18z+19w=20e

and return x,y,z,w?

I was trying to follow the format described in this answer, Currently what I have is the following code which which throws IllegalArgumentException: "java.lang.IllegalArgumentException: Can't solve for wide systems. More variables than equations. when it attempts to calculate the 4 results:

                    double[20] args = {1,2,3... ,20};
                    SimpleMatrix A = new SimpleMatrix(4,5);
                    SimpleMatrix b = new SimpleMatrix(4,1);
                    int val=0;
                    for(int i =0;i<4;i++){
                        for(int j=0;j<5;j++){
                            A.setRow(i, j, args[val]);
                            val++;
                        }
                        b.setRow(i,0, args[val-1]);
                    }
                    double[] result = new double[4];  //results for x y z w
                    try {
                        SimpleMatrix solution = A.solve(b);   //throws IllegalArgumentException!
                        for(int i=0;i<solution.getNumElements();i++) {
                            result[i] = solution.get(i, 0);
                        }

                        --print results--
                    }
                    catch ( SingularMatrixException e ) {
                       throw new IllegalArgumentException();
                    }

What am I doing wrong?

Answer 1

I think it may have to do with your matrix dimensions.

new SimpleMatrix A(4,5) should be replaced with new SimpleMatrix A(4,4).