public static unsafe double[][] Dot(this long[,] a, double[][] b, double[][] result)
{
int N = result.Length;
int K = a.Columns();
int M = result.Columns();
var t = new double[K];
fixed(long *A = a)
for (int j = 0; j < M; j++)
{
for (int k = 0; k < t.Length; k++)
{
t[k] = b[k][j];
}
long *pa = A;
for (int i = 0; i < N; i++)
{
double s = (double)0;
for (int k = 0; k < t.Length; k++)
{
s += (double)((double)(*pa++) * (double)t[k]);
}
result[i][j] = (double)s;
}
}
return(result);
}