code: public static VectorFunction asMulFunction(final double arg) {
          return new VectorFunction() {
              @Override
              public double evaluate(int i, double value) {
                  return value * arg;
              }
          };
      }
docs: Creates a mul function that multiplies given {@code value} by it's argument.
  
  @param arg a value to be multiplied by function's argument
  
  @return a closure that does {@code _ * _}