public static function Pnm06a($date1, $date2, array &$rnpb) {
    $gamb;
    $phib;
    $psib;
    $epsa;
    $dp;
    $de;

    /* Fukushima-Williams angles for frame bias and precession. */
    IAU::Pfw06($date1, $date2, $gamb, $phib, $psib, $epsa);

    /* Nutation components. */
    IAU::Nut06a($date1, $date2, $dp, $de);

    /* Equinox based nutation x precession x bias matrix. */
    IAU::Fw2m($gamb, $phib, $psib + $dp, $epsa + $de, $rnpb);

    return;
  }