What is the alternative method for Diag(k) in C++?

Question

I'm converting a matlab code to C++ code and trying to find a function in Lapack, Blas or even Atlas that does the same job at Diag(k) function in matlab ? Any suggestions ?

"`Diag(k)`"? Do you mean, creation of a diagonal matrix from a vector or extraction of the diagonal of any matrix as a vector? — leftaroundabout, Apr 12 '12 at 18:49
... and the answer depends on how you represent matrices and vector in C++. In particular, what is the type of `k`? Either way, you don't need Blas or Lapack (ATLAS is just an implementation of these) for this, as all it is a simple looping over an index : `for ( i=0; i — sly, Apr 12 '12 at 20:15

score 0 · Answer 1 · answered Apr 13 '12 at 03:08

GSL, the Gnu Scientific Library has a function gsl_matrix_diagonal (gsl_matrix * m). This creates a "vector view" into the matrix which is more or less a gsl vector aliased to the diagonal of the matrix. Dunno if you love GSL, but it also includes BLAS support. I think it's a very good library.

score 0 · Accepted Answer · answered Apr 13 '12 at 12:38

static void create_diagonal_matrix(T* matrix,T* v,int size)
    {   
        for(int i=0;i<size;i++)
        {
            for(int32_t j=0;j<size;j++)
            {
                if(i==j)
                    matrix[j*size+i]=v[i];
                else
                    matrix[j*size+i]=0;
            }
        }
    }

What is the alternative method for Diag(k) in C++?

2 Answers2