我正在寻找一种在Javascript中计算累积分布函数的方法。是否有已经实现了此功能的类库?您有想法如何使其工作吗?它不需要100%准确,但我需要一个大致的值。
http://en.wikipedia.org/wiki/Cumulative_distribution_function
我正在寻找一种在Javascript中计算累积分布函数的方法。是否有已经实现了此功能的类库?您有想法如何使其工作吗?它不需要100%准确,但我需要一个大致的值。
http://en.wikipedia.org/wiki/Cumulative_distribution_function
function normalcdf(mean, sigma, to)
{
var z = (to-mean)/Math.sqrt(2*sigma*sigma);
var t = 1/(1+0.3275911*Math.abs(z));
var a1 = 0.254829592;
var a2 = -0.284496736;
var a3 = 1.421413741;
var a4 = -1.453152027;
var a5 = 1.061405429;
var erf = 1-(((((a5*t + a4)*t) + a3)*t + a2)*t + a1)*t*Math.exp(-z*z);
var sign = 1;
if(z < 0)
{
sign = -1;
}
return (1/2)*(1+sign*erf);
}
normalcdf(30, 25, 1.4241); //-> 0.12651187738346226
//wolframalpha.com 0.12651200000000000
math.js库提供了一个erf
函数。根据在Wolfram Alpha找到的定义,cdfNormal
函数可以用以下Javascript代码实现:
const mathjs = require('mathjs')
function cdfNormal (x, mean, standardDeviation) {
return (1 - mathjs.erf((mean - x ) / (Math.sqrt(2) * standardDeviation))) / 2
}
在 node.js
控制台:
> console.log(cdfNormal(5, 30, 25))
> 0.15865525393145707 // Equal to Wolfram Alpha's result at: https://sandbox.open.wolframcloud.com/app/objects/4935c1cb-c245-4d8d-9668-4d353ad714ec#sidebar=compute
这个公式会给出正确的正态分布函数值,而不像当前被接受的答案那样
function ncdf(x, mean, std) {
var x = (x - mean) / std
var t = 1 / (1 + .2315419 * Math.abs(x))
var d =.3989423 * Math.exp( -x * x / 2)
var prob = d * t * (.3193815 + t * ( -.3565638 + t * (1.781478 + t * (-1.821256 + t * 1.330274))))
if( x > 0 ) prob = 1 - prob
return prob
}
这是一种暴力实现,但可以提高更多精度位数。上述逼近值在10^-7内准确。我的实现速度较慢(700纳秒),但精度在10^-14范围内。normal(25,30,1.4241) === 0.00022322110257305683,相比 Wolfram 的 0.000223221102572082 更为准确。
它采用标准正态分布的幂级数即钟形曲线,然后对级数进行积分计算。
我最初是用C语言编写的,所以我承认在JavaScript中有些优化看起来可能有些愚蠢。
function normal(x, mu, sigma) {
return stdNormal((x-mu)/sigma);
}
function stdNormal(z) {
var j, k, kMax, m, values, total, subtotal, item, z2, z4, a, b;
// Power series is not stable at these extreme tail scenarios
if (z < -6) { return 0; }
if (z > 6) { return 1; }
m = 1; // m(k) == (2**k)/factorial(k)
b = z; // b(k) == z ** (2*k + 1)
z2 = z * z; // cache of z squared
z4 = z2 * z2; // cache of z to the 4th
values = [];
// Compute the power series in groups of two terms.
// This reduces floating point errors because the series
// alternates between positive and negative.
for (k=0; k<100; k+=2) {
a = 2*k + 1;
item = b / (a*m);
item *= (1 - (a*z2)/((a+1)*(a+2)));
values.push(item);
m *= (4*(k+1)*(k+2));
b *= z4;
}
// Add the smallest terms to the total first that
// way we minimize the floating point errors.
total = 0;
for (k=49; k>=0; k--) {
total += values[k];
}
// Multiply total by 1/sqrt(2*PI)
// Then add 0.5 so that stdNormal(0) === 0.5
return 0.5 + 0.3989422804014327 * total;
}
NORMSDIST
函数相同的结果,而我发现其他所有函数都给我不同的结果。 - Max它提供了标准正态分布、学生t分布、f分布和卡方分布的CDF和反CDF的javascript实现。
使用js库获取CDF和反CDF:
jsstats = require('js-stats');
//====================NORMAL DISTRIBUTION====================//
var mu = 0.0; // mean
var sd = 1.0; // standard deviation
var normal_distribution = new jsstats.NormalDistribution(mu, sd);
var X = 10.0; // point estimate value
var p = normal_distribution.cumulativeProbability(X); // cumulative probability
var p = 0.7; // cumulative probability
var X = normal_distribution.invCumulativeProbability(p); // point estimate value
//====================T DISTRIBUTION====================//
var df = 10; // degrees of freedom for t-distribution
var t_distribution = new jsstats.TDistribution(df);
var t_df = 10.0; // point estimate or test statistic
var p = t_distribution.cumulativeProbability(t_df); // cumulative probability
var p = 0.7;
var t_df = t_distribution.invCumulativeProbability(p); // point estimate or test statistic
//====================F DISTRIBUTION====================//
var df1 = 10; // degrees of freedom for f-distribution
var df2 = 20; // degrees of freedom for f-distribution
var f_distribution = new jsstats.FDistribution(df1, df2);
var F = 10.0; // point estimate or test statistic
var p = f_distribution.cumulativeProbability(F); // cumulative probability
//====================Chi Square DISTRIBUTION====================//
var df = 10; // degrees of freedom for cs-distribution
var cs_distribution = new jsstats.ChiSquareDistribution(df);
var X = 10.0; // point estimate or test statistic
var p = cs_distribution.cumulativeProbability(X); // cumulative probability