Wrong Results in from LAPACK in Fortran

I installed LAPACK in Msys2 by pasting the command from this link: https://packages.msys2.org/package/mingw-w64-x86_64-lapack. I then linked the library with -llapack -lblas. Everything seems to work fine, but every time I use the subroutines from LAPACK, I get incorrect results.

For example, the subroutine DGESV. I tried many different input values, but all resulted in incorrect answers. Does anyone know why I'm getting these results?

I've tried different values (different matrices) and I've searched for answers online, without succes.

relevant Code:

 call DGESV(N, 1, K, N, U_step, FRes, N, info)
 if (info /= 0) then
        write(*,*) "Error while Solving Matrix"
        stop
 end if

• K is a quadratic Matrix (N x N)
• U_step is the result vector
• FRes is the right side Vector

Basically in the Form Ax = B --> KU_step = FRes

Example of wrong results:

K =

FRes =

I just didn't trusted Matlab, I crosschecked the results in Wolfram Alpha.

You are visibly expecting the result in the 5th argument of DGESV, but DEGSV actually outputs the result in the 6th argument, hence overwriting the input right hand side vector(s).

The 5th argument is a work integer array where DEGSV stores the pivot indices of the LU decomposition.

So your code should be something like:

integer :: ipiv(N)
...
U_step(:) = FRes(:)
call DGESV(N, 1, K, N, ipiv, U_step, N, info)

DGESV documentation: https://netlib.org/lapack/explore-html/d7/d3b/group__double_g_esolve_ga5ee879032a8365897c3ba91e3dc8d512.html