How to get real value in math function

Question

How to get real value in math function

Hello everyone, I have this code that does functions in math, but with this function, the result is wrong oO

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

Operation Evaluado 1: 4

I have some other code that I did

/*
 * 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 want to use

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

because it is a library and I think it is more accurate and I don’t want to use my code because there are many lines and I don’t know if it is 100% efficient. can someone help me? or give me a recommendation to allow these math functions? many thanks

+3

java javascript

Alien Java Apr 13 17 at 4:09

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3 answers

I think your program is going by evaluating

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

because an operator ^

in computer science means bitwise exception or, which basically means the bits are 1 or 0 and then change them to 0, otherwise 1. And 2 is represented 10

and 0 is 0

, so2^0 = 2

Try replacing ^2

with *X

, alternatively you can use Math.pow(X,n)

if you need a degree of elevation to some power n

, but for squaring it is better to just write it asX*X

Below is deprecation due to changes in the question, but 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 another user's answer. 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);

0

Matthew ciaramitaro Apr 13 17 at 4:15 am

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You have the wrong syntax for food. Replace -3*X^2-16*X+2

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

. See Javascript. What does the ^ (caret) operator do?

0

Ville oikarinen Apr 13 17 at 4:17

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Robby cornelissen · Accepted Answer · 2017-04-13T04:16:35+0000

The result you are getting is correct.

The confusion arises from the fact that what you think of as the force operator ( ^

) is actually the bitwise XOR operator in JavaScript (you are using a JavaScript script).

So, the estimate 0 ^ 2

gives 2

, and when the estimate is Math.pow(0, 2)

obtained 0

, therefore, the difference.

To get the expected result, the expression would have to read:

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

You can preprocess the expression to replace exponential operations with calls 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"

Run code Hide result

Using a script engine it might look like this:

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 Java's regular expression replacement:

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

How to get real value in math function

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