code: public static double acot(double value) {
          if (value == 0) {
              return Double.NaN;
          } else if (value > 0) {
              return atan(1 / value);
          } else {
              return atan(1 / value) + PI;
          }
      }
docs: Calculates the arc cotangent of the value specified<br><br> Returns NaN if the input value is outside the cotangent range
  
  @param value of the cotangent
  @return cotangent arc in radians