FBCache unnecessary allocation

[alphaville]

In FBCache the following piece of code has the following problem:

if (m_prob.f1() != NULL) {
        Matrix gradf1_diff = Matrix(m_x_rows, m_x_cols);
        if (m_prob.L1() != NULL) {
            Matrix gradf1_L1diff = Matrix(m_prob.L1()->dimensionOut());
            gradf1_diff = m_prob.L1()->callAdjoint(gradf1_L1diff);
        } else {

        }
        Matrix::add(*m_gradFBEx, -1.0, gradf1_diff, 1.0 / gamma);
    }

The line

Matrix gradf1_diff = Matrix(m_x_rows, m_x_cols);

allocates memory for a dense matrix. Then, line

gradf1_diff = m_prob.L1()->callAdjoint(gradf1_L1diff);

computes the value of the adjoint of L1 at gradf1_L1diff and copies the value to gradf1_diff!
This happens with the invocation of Matrix::operator=. Notice that would be different to do

Matrix gradf1_diff = m_prob.L1()->callAdjoint(gradf1_L1diff);