@Test
public void testLeftVectors() {

  Matrix A = lowRankMatrix();
  SequentialBigSvd s = new SequentialBigSvd(A, 8);
  SingularValueDecomposition svd = new SingularValueDecomposition(A);
  // can only check first few singular vectors because once the singular values
  // go to zero, the singular vectors are not uniquely determined
  Matrix u1 = svd.getU().viewPart(0, 20, 0, 4).assign(Functions.ABS);
  Matrix u2 = s.getU().viewPart(0, 20, 0, 4).assign(Functions.ABS);
  assertEquals(0, u1.minus(u2).aggregate(Functions.PLUS, Functions.ABS), 1.0e-9);
}