I am having trouble with the output ipiv from dgetrf. My understanding is that it should return an array the length of the number of rows of my input matrix. Each member of this array should contain a different number. These numbers are the column in which a 1 would be placed for the corresponding column i.e. if:
ipiv =
1
4
5
2
3
This would correspond to a permutation matrix that looks like:
1 0 0 0 0
0 0 0 1 0
0 0 0 0 1
0 1 0 0 0
0 0 1 0 0
And that this permutation matrix P*X(my input matrix) = L*U. However, the ipiv outputs I get from dgetrf have many repetititions such as the output below and P*X != L*U:
ipiv = 4
ipiv = 2
ipiv = 4
ipiv = 4
ipiv = 5
Here is my example program:
#define M 5
#define N 5
int main()
{
int i,m, n, *ipiv, info;
double a[M*N] = { 3, 4, 6, 8, 2, 2, 9, 6, 1, 8, 12, 8, 4, 6, 2, 6, 6, 7, 1, 2, 9, 4, 3, 2, 8 };
ipiv = malloc(M*sizeof(int));
m = M;
n = N;
info = 0;
dgetrf(&m,&n,a,&m,ipiv,&info);
printf("info = %d\\n",info);
for (i=0;i
{
printf("ipiv = %d\\n",ipiv
);
}
return(0);
}
Thanks!
