javascript - 如何获得数学函数的真实值

Question

大家好，我有这段代码可以在数学中生成函数，但是这个函数的结果是错误的 o.O

x=0

"-3*X^2-16*X+2"

代码:

public static void main(String[] args) throws Exception {

        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("js");
        engine.put("X", 0);

        Object operation = engine.eval("-3*X^2-16*X+2");
        //Object operation2 = engine.eval("(X+3)");

        System.out.println("Evaluado operacion 1: " + operation);
        //System.out.println("Evaluado operacion 2: " + operation2);

    }

结果是 2 但我得到 4

Evaluado operacion 1: 4

我还有其他的代码

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package gustavo_santa;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import javax.swing.JOptionPane;

/**
 *
 * @author osmarvirux
 */
public class SerieB {
    //xi and x4
    int xi;
    int x4;
    //f(x) function variables
    String positive_negative;
    int num_one;
    int elevation_one;
    String add_subtract_one;
    int num_two;
    int elevation_two;
    String add_subtract_two;
    int num_three;
    //results
    String xi_result;
    String x4_result;

    public SerieB(int xi, int x4, String positive_negative, int num_one, int elevation_one, String add_subtract_one, int num_two, int elevation_two, String add_subtract_two, int num_three) {
        this.xi = xi;
        this.x4 = x4;
        this.positive_negative = positive_negative;
        this.num_one = num_one;
        this.elevation_one = elevation_one;
        this.add_subtract_one = add_subtract_one;
        this.num_two = num_two;
        this.elevation_two = elevation_two;
        this.add_subtract_two = add_subtract_two;
        this.num_three = num_three;
    }

    public void Procedure_xi(){
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("js");
        if (positive_negative == "-"){

           try {
            xi_result=(num_one*(Math.pow(xi, elevation_one)))+add_subtract_one+(num_two*(Math.pow(xi, elevation_two)))
                    +add_subtract_two+num_three;
            Object result = engine.eval(xi_result);
            System.out.println(xi_result+" = "+result);
            } catch(ScriptException se) {
                se.printStackTrace();
            }           
        }else{
             try {
            xi_result=((-num_one*(Math.pow(xi, elevation_one)))+add_subtract_one+(num_two*(Math.pow(xi, elevation_two)))
            +add_subtract_two+num_three);
            Object result = engine.eval(xi_result);
            System.out.println(xi_result+" = "+result);
            } catch(ScriptException se) {
                se.printStackTrace();
            }       

        }
    }
    public void Procedure_x4(){
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("js");
        if (positive_negative == "-"){

           try {
            x4_result=(num_one*(Math.pow(x4, elevation_one)))+add_subtract_one+(num_two*(Math.pow(x4, elevation_two)))
                    +add_subtract_two+num_three;
            Object result = engine.eval(x4_result);
            System.out.println(x4_result+" = "+result);
            } catch(ScriptException se) {
                se.printStackTrace();
            }           
        }else{
             try {
            x4_result=((-num_one*(Math.pow(x4, elevation_one)))+add_subtract_one+(num_two*(Math.pow(x4, elevation_two)))
            +add_subtract_two+num_three);
            Object result = engine.eval(x4_result);
            System.out.println(x4_result+" = "+result);
            } catch(ScriptException se) {
                se.printStackTrace();
            }       

        }
    }
    public static void main(String[] args){
        //-3x^2-16x+2
        SerieB obj = new SerieB(0, 1, "+", -3, 2, "-", 16, 1, "+", 2);
        obj.Procedure_xi();
        obj.Procedure_x4();
    }


}

此代码的结果是 2 但我想使用

ScriptEngineManager manager = new ScriptEngineManager();ScriptEngineManager manager = new ScriptEngineManager();

因为是一个库，我认为它更精确，我不想使用我的代码，因为有很多行而且我不知道是否 100% 有效。有人可以帮助我吗？或者给我一个解决这个数学函数的建议？非常感谢

Answer 1

您得到的结果是正确的。

之所以会产生混淆，是因为您假设的幂运算符 (^) 实际上是 bitwise XOR JavaScript 中的运算符(您正在使用 JavaScript 脚本引擎)。

因此，评估 0 ^ 2 会产生 2，而评估 Math.pow(0, 2) 会产生 0，因此有所不同。

要获得您期望的结果，表达式必须为:

-3*Math.pow(X,2)-16*X+2

您可以预处理表达式以调用 Math.pow() 来替换指数运算:

let X = 0;
let expression = "-3*X^2-16*X+2"
let processed = expression.replace(/(\w+)\^(\w+)/g, 'Math.pow($1,$2)');

console.log(processed); // prints "-3*Math.pow(X,2)-16*X+2"
console.log(eval(processed)); // prints "2"

使用脚本引擎，它看起来像:

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("js");
engine.put("X", 0);
engine.put("expression", "-3*X^2-16*X+2");
engine.put("processed", engine.eval("expression.replace(/(\\w+)\\^(\\w+)/g, 'Math.pow($1,$2)')"));

System.out.println(engine.eval("eval(processed)")); // 2.0

或者，如果您更喜欢在 Java 中进行正则表达式替换:

String expression = "-3*X^2-16*X+2";
String processed = expression.replaceAll("(\\w+)\\^(\\w+)", "Math.pow($1,$2)");

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("js");
engine.put("X", 0);

System.out.println(engine.eval(processed)); // 2.0