docs: public int indexOfFromTo(double element, int from, int to) {
  	// overridden for performance only.
  	if (size==0) return -1;
  	checkRangeFromTo(from, to, size);
  
  	double[] theElements = elements;
  	for (int i = from ; i <= to; i++) {
  	    if (element==theElements[i]) {return i;} //found
  	}
  	return -1; //not found
  }