copy a column of matrix to a vector

[aiminy]

I am using C++ to call LAPACK.
I am using dgemm_()
I am new to LAPACK.
now I want to code something like this:

double a[n*n],b[n*1]
for(k=0; k<n;k++)
{
a(1:n,k)=a(n,n)*a(1:n,k)-b(k)*a(1:n,k)
e[k]=dot_product(a(1:n,k))
}

Does anyone know hoe to code this using dgemm_ in C++ ?