Question

I need to get the solution of an equation system. For this purpose i use the function sgesv_().

Everything works great, and it retur me the right results of the solution.

But i get an strange Warning.

warning: passing argument 3 of ‘sgesv_’ from incompatible pointer type

I am using the function as Apple use it on the WWDC video.

What am I doing wrong?

a1,a2,b1,b2,c1,c2 are floats

        __CLPK_integer info;
        __CLPK_integer n=2;
        __CLPK_integer nb=1;
        __CLPK_integer ipiv[n];
        float A[n][n];
        A[0][0]=a1;
        A[0][1]=a2;
        A[1][0]=b1;
        A[1][1]=b2;
        float B[n];
        B[0]=-c1;
        B[1]=-c2;
        sgesv_(&n, &nb, A, &n, ipiv, B, &n, &info);

Answer 1

The third parameter is meant to be a float * but you’re passing a 2D array of float. It just so happens that these floats are in the right order. To get rid of the warning you can do this:

    sgesv_(&n, &nb, &A[0][0], &n, ipiv, B, &n, &info);

or this:

    sgesv_(&n, &nb, A[0], &n, ipiv, B, &n, &info);

or even this:

    sgesv_(&n, &nb, (float *)A, &n, ipiv, B, &n, &info);

Or you could just “flatten” your A array, e.g.

    float A[n * n];
    A[0 * n + 0] = a1;
    A[0 * n + 1] = a2;
    A[1 * n + 0] = b1;
    A[1 * n + 1] = b2;
    // ...
    sgesv_(&n, &nb, A, &n, ipiv, B, &n, &info);