Node.js Math.random（）不起作用

Question

我写了这段代码来使用Monte Carlo模拟来估计Pi，但我注意到无论迭代的数量如何，结果总是在2.0左右。我想这可能是Math.random（）不起作用。 代码使用Node v7.5.0在Mac OS Sierra上运行。

任何想法？

// Begin of code 
iterations = 100000000; 
in_circle = 0; 


function find_pi(){ 
    for (i = 0; i < iterations; i++){ 
     x = 1 - 2 * Math.random(); 
     y = 1 - 2 * Math.random(); 

     if ((x^2 + y^2) < 1) 
      in_circle++; 
    } 

    console.log("in_circle = ", in_circle); 
    console.log("iterations = ", iterations); 
    console.log("Estimated PI Value = ", 4 * in_circle/iterations); 
} 

var startTime = Date.now(); 
find_pi(); 
var endTime = Date.now(); 
console.log("\n===== Took us: " + (endTime - startTime) + " milliseconds"); 

Answer 1

x^2是不幂，这是bitwise XOR。

要进行取幂，请使用x*x，Math.pow(x,2)或x**2。如果你这样做，你会正确地估计π≈3.14：

// Begin of code 
 
iterations = 100000; 
 
in_circle = 0; 
 

 

 
function find_pi(){ 
 
    for (i = 0; i < iterations; i++){ 
 
     x = 1 - 2 * Math.random(); 
 
     y = 1 - 2 * Math.random(); 
 

 
     if ((x*x + y*y) < 1) 
 
      in_circle++; 
 
    } 
 

 
    console.log("in_circle = ", in_circle); 
 
    console.log("iterations = ", iterations); 
 
    console.log("Estimated PI Value = ", 4 * in_circle/iterations); 
 
} 
 

 
var startTime = Date.now(); 
 
find_pi(); 
 
var endTime = Date.now(); 
 
console.log("\n===== Took us: " + (endTime - startTime) + " milliseconds");