//-------------------------------------------------------------------------
 public virtual void test_diagonal()
 {
     assertMatrix(DoubleMatrix.diagonal(DoubleArray.EMPTY));
     assertMatrix(DoubleMatrix.diagonal(DoubleArray.of(2d, 3d, 4d)), 2d, 0d, 0d, 0d, 3d, 0d, 0d, 0d, 4d);
     assertEquals(DoubleMatrix.diagonal(DoubleArray.of(1d, 1d, 1d)), DoubleMatrix.identity(3));
 }