code: public static LinearTransformationBuilder mapping(double x1, double y1) {
      checkArgument(isFinite(x1) && isFinite(y1));
      return new LinearTransformationBuilder(x1, y1);
    }
docs: Start building an instance which maps {@code x = x1} to {@code y = y1}. Both arguments must be
  finite. Call either {@link LinearTransformationBuilder#and} or {@link
  LinearTransformationBuilder#withSlope} on the returned object to finish building the instance.