How to get the real value in a mathematic function

Question

hello everyone i have this code that makes functions in mathematics but with this function the result is wrong o.O

x=0

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

Code:

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);

    }

the result is 2 but i get 4

Evaluado operacion 1: 4

i have other code that i made

/*
 * 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();
    }


}

the result with this code is 2 but i wanna use

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

because is a library and i think is more precise and i dont wanna use my code because there are many lines and i dont know if is 100% efficient. someone can help me? or give me a recomendation to resolve this mathematic functions? thanks a lot

The issue is that `^` means bitwise exclusive or, rather than exponentiation. But I don't know how to fix this. — Dawood ibn Kareem, Apr 13 '17 at 04:15
Consider adding a JavaScript tag to this question since you're using a JavaScript script engine. — Robby Cornelissen, Apr 13 '17 at 04:27

Robby Cornelissen · Accepted Answer · 2017-04-13T04:49:17.600

1

The result you're getting is correct.

The confusion arises from the fact that what you're assuming to be the power operator (^) is actually the bitwise XOR operator in JavaScript (you're using a JavaScript script engine).

So, evaluating 0 ^ 2 yields 2, while evaluating Math.pow(0, 2) yields 0, hence the difference.

To get the result you expect, the expression would have to read:

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

You could pre-process the expression to replace the exponential operations with invocations of Math.pow():

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"

Using the script engine, that could look like:

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

Or, if you prefer to do the regular expression replacement in Java:

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

edited Apr 13 '17 at 04:49

answered Apr 13 '17 at 04:16

Robby Cornelissen

91,784
22
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`Math.pow(0,2)` means 0 to the power of 2 which should yield 0 not 1 – Matthew Ciaramitaro Apr 13 '17 at 04:23
but i wanna get the information of a String how would be the text? because the user cant write "-3*Math.pow(X,2)-16*X+2" in a string brother :( – Alien Java Apr 13 '17 at 04:24
@MatthewCiaramitaro Thx. Typo. – Robby Cornelissen Apr 13 '17 at 04:24
1

@AlienJava See the last part of my answer – Robby Cornelissen Apr 13 '17 at 04:25
1

@AlienJava Don't add answers or partial answers to your question. I'll update my answer with a Java snippet – Robby Cornelissen Apr 13 '17 at 04:32
@AlienJava that text should be applied to the String inside the eval not to the Object you created. the string must be changed before you evaluate it – Matthew Ciaramitaro Apr 13 '17 at 04:32
@RobbyCornelissen AWESOME SR!! – Alien Java Apr 13 '17 at 04:49
@AlienJava Now please remove the partial answer from your question. Your question stands as is, so does my answer. – Robby Cornelissen Apr 13 '17 at 04:52
@RobbyCornelissen im sorry i dont undertand at all brother im a little noob in stackoverflow and im not a native english speaker. can you be more specific? – Alien Java Apr 13 '17 at 04:56
The point is: things get really confusing if you start adding answers or partial answers to your question. Roll it back to its original state. – Robby Cornelissen Apr 13 '17 at 04:58
1

Delete everything including and after "i tried with this but i get syntax error :( im using netbeans (java 8.1)" – Matthew Ciaramitaro Apr 13 '17 at 04:59
@RobbyCornelissen brother i already updated the question, Matthew Ciaramitaro helped me with his information. did i do the correct? or do you wanna i delete more information? – Alien Java Apr 13 '17 at 05:04
@AlienJava Looks great, thanks. I even gave you my upvote back :) – Robby Cornelissen Apr 13 '17 at 05:04
@RobbyCornelissen can you help me with one exercise? i can pay you some dollars with paypal teacher! please i believe 1 day you finish it.. in java. i hope your answer – Alien Java Apr 13 '17 at 20:34

Matthew Ciaramitaro · Answer 2 · 2017-04-13T05:16:48.507

0

I think what's happening is your program is evaluating

(-3*0)^2 - 16*0 + 2 = 0^2 +2 = 2+2 =4

because the operator ^ in computer science mean bitwise exclusive or, which basically means if the bits are both 1 or 0 then change them to 0, else 1. And 2 is represented by 10 while 0 is 0 so 2^0 = 2

Try replacing ^2 with *X alternatively you can use Math.pow(X,n) , if you need exponentiation to some power n, but for squaring it's better to just write it out as X*X

The Below is Outdated Due to Edits to Question, but is still functional:

In the second part of your question you wrote

Object operation = engine.eval("-3*(X^2)-16*X +2");
String processed = operation.replace(/(\w+)\^(\w+)/g, 'Math.pow($1,$2)');

based on an answer by another user. You should have written

String expr = "-3*(X^2)-16*X +2";
String processed = expr.replaceAll("(\\w+)(\\^)(\\w+)", 'Math.pow($1,$2'));
Object operation = engine.eval(processed);

edited Apr 13 '17 at 05:16

answered Apr 13 '17 at 04:15

Matthew Ciaramitaro

1,184
1
13
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That won't compile. – Robby Cornelissen Apr 13 '17 at 04:42
Is that a regex thing? – Matthew Ciaramitaro Apr 13 '17 at 04:43
ya Ik... give me a sec – Matthew Ciaramitaro Apr 13 '17 at 04:46
I just finished and noticed you'd already added this version to your answer.... that's what I get for being slow – Matthew Ciaramitaro Apr 13 '17 at 04:57

score 0 · Answer 3 · edited May 23 '17 at 12:10

0

You have incorrect syntax for power. Replace -3*X^2-16*X+2 with -3*Math.pow(X,2)-16*X+2. See Javascript, What does the ^ (caret) operator do?

edited May 23 '17 at 12:10

Community

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answered Apr 13 '17 at 04:17

Ville Oikarinen

400
1
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How to get the real value in a mathematic function

3 Answers3