/** <tt>a + b/constant</tt>. */
 public static DComplexPlusMultSecond plusDiv(final double[] constant) {
   return new DComplexPlusMultSecond(DComplex.inv(constant));
 }
 /** <tt>a - b*constant</tt>. */
 public static DComplexPlusMultSecond minusMult(final double[] constant) {
   return new DComplexPlusMultSecond(DComplex.neg(constant));
 }