How to get the transform matrix for balanced truncation?

The built-in function 'reduce' and 'balancmr' seem don't provide the transform matrix for balanced truncation. I'm wondering is there a way to figure out the transform matrix? I mean the V (N by k) for (V'*A*V=A_r,V'*B=B_r,C*V=C_r,X=V*X_r,V'*V=I) suppose I already know A,B,C and A_r,B_r,C_r. Thanks!