I have one cx_mat, "cx_mat X" ,i need convert X.real() to double xr[], and X.imag() to double xi[], how can i do it fastly?
Thank you

What is cx_mat? Anyway, assuming it's equivalent to a MatrixXcd, if you want to extract the real and imaginary part as sequential buffers, then you first need to copy them to MatrixXd:

MatrixXcd X;
MatrixXd R, I;
R = X.real();
I = X.imag();
double* xr = R.data();
double* xi = I.data();

If you can deal with interleaved real/imag parts, then:

double* xr = &numext::real_ref(X(0,0));
double* xi = xr+1;

and then:

i-th real part == xr[2*i]
i-th imag part == xi[2*i]