@Test
public void testGemvSparse() throws Exception {

    DenseVector y1 = DenseVector.ones(2);
    BLAS.gemv(2.0, mat, false, spv2, 0., y1);
    Assert.assertArrayEquals(new double[]{20, 44}, y1.data, TOL);
    DenseVector y2 = DenseVector.ones(2);
    BLAS.gemv(2.0, mat, false, spv2, 1., y2);
    Assert.assertArrayEquals(new double[]{21, 45}, y2.data, TOL);
}