zpteqr function

Implementation

void zpteqr(
  final String COMPZ,
  final int N,
  final Array<double> D_,
  final Array<double> E_,
  final Matrix<Complex> Z_,
  final int LDZ,
  final Array<double> WORK_,
  final Box<int> INFO,
) {
  final Z = Z_.having(ld: LDZ);
  final D = D_.having();
  final E = E_.having();
  final WORK = WORK_.having();
  final C = Matrix<Complex>(1, 1), VT = Matrix<Complex>(1, 1);
  int I, ICOMPZ, NRU;

  // Test the input parameters.

  INFO.value = 0;

  if (lsame(COMPZ, 'N')) {
    ICOMPZ = 0;
  } else if (lsame(COMPZ, 'V')) {
    ICOMPZ = 1;
  } else if (lsame(COMPZ, 'I')) {
    ICOMPZ = 2;
  } else {
    ICOMPZ = -1;
  }
  if (ICOMPZ < 0) {
    INFO.value = -1;
  } else if (N < 0) {
    INFO.value = -2;
  } else if ((LDZ < 1) || (ICOMPZ > 0 && LDZ < max(1, N))) {
    INFO.value = -6;
  }
  if (INFO.value != 0) {
    xerbla('ZPTEQR', -INFO.value);
    return;
  }

  // Quick return if possible

  if (N == 0) return;

  if (N == 1) {
    if (ICOMPZ > 0) Z[1][1] = Complex.one;
    return;
  }
  if (ICOMPZ == 2) zlaset('Full', N, N, Complex.zero, Complex.one, Z, LDZ);

  // Call DPTTRF to factor the matrix.

  dpttrf(N, D, E, INFO);
  if (INFO.value != 0) return;
  for (I = 1; I <= N; I++) {
    D[I] = sqrt(D[I]);
  }
  for (I = 1; I <= N - 1; I++) {
    E[I] *= D[I];
  }

  // Call ZBDSQR to compute the singular values/vectors of the
  // bidiagonal factor.

  if (ICOMPZ > 0) {
    NRU = N;
  } else {
    NRU = 0;
  }
  zbdsqr('Lower', N, 0, NRU, 0, D, E, VT, 1, Z, LDZ, C, 1, WORK, INFO);

  // Square the singular values.

  if (INFO.value == 0) {
    for (I = 1; I <= N; I++) {
      D[I] *= D[I];
    }
  } else {
    INFO.value = N + INFO.value;
  }
}