public ComplexDouble subi(ComplexDouble c, ComplexDouble result) {
    if (this == result) {
      r -= c.r;
      i -= c.i;
    } else {
      result.r = r - c.r;
      result.i = i - c.i;
    }
    return this;
  }
public ComplexDouble subi ( ComplexDouble c , ComplexDouble result ) { if ( this == result ) { r -= c . r ; i -= c . i ; } else { result . r = r - c . r ; result . i = i - c . i ; } return this ; }
Subtract two complex numbers, in-place

@param c      complex number to subtract
@param result resulting complex number
@return same as result