We present an algorithm to solve the CASSCF linear response equations that is
both simple and efficient. The algorithm makes use of the well established
symmetric and antisymmetric combinations of trial vectors, but further
orthogonalizes them with respect to the scalar product induced by the response
matrix. This leads to a standard, symmetric, block eigenvalue problem in the
expansion subspace that can be solved by diagonalizing a symmetric, positive
definite matrix half the size of the expansion space. Preliminary numerical
tests show that the algorithm is robust and stable