@Test
public void testLSolve() {

    Matrix X = new Matrix(5, 8);
    X.randomize();
    Matrix S = SymmetricMatrix.XXt(X);
    Matrix A = new Matrix(3, 5);
    A.randomize();
    Matrix B1 = A.clone();
    Matrix B2 = Matrix.lsolve(S.subMatrix(), A.subMatrix());
    SymmetricMatrix.lsolve(S, B1.subMatrix(), true);
    Matrix D = B1.minus(B2);
    assertTrue(D.nrm2() < 1e-9);
}