time-to-botec

Benchmark sampling in different programming languages
Log | Files | Refs | README

skewness.js (2075B)

      1 /**
      2 * @license Apache-2.0
      3 *
      4 * Copyright (c) 2018 The Stdlib Authors.
      5 *
      6 * Licensed under the Apache License, Version 2.0 (the "License");
      7 * you may not use this file except in compliance with the License.
      8 * You may obtain a copy of the License at
      9 *
     10 *    http://www.apache.org/licenses/LICENSE-2.0
     11 *
     12 * Unless required by applicable law or agreed to in writing, software
     13 * distributed under the License is distributed on an "AS IS" BASIS,
     14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     15 * See the License for the specific language governing permissions and
     16 * limitations under the License.
     17 */
     18 
     19 'use strict';
     20 
     21 // MODULES //
     22 
     23 var isNonNegativeInteger = require( '@stdlib/math/base/assert/is-nonnegative-integer' );
     24 var sqrt = require( '@stdlib/math/base/special/sqrt' );
     25 var PINF = require( '@stdlib/constants/float64/pinf' );
     26 
     27 
     28 // MAIN //
     29 
     30 /**
     31 * Returns the skewness of a hypergeometric distribution.
     32 *
     33 * @param {NonNegativeInteger} N - population size
     34 * @param {NonNegativeInteger} K - subpopulation size
     35 * @param {NonNegativeInteger} n - number of draws
     36 * @returns {number} skewness
     37 *
     38 * @example
     39 * var v = skewness( 16, 11, 4 );
     40 * // returns ~-0.258
     41 *
     42 * @example
     43 * var v = skewness( 4, 2, 2 );
     44 * // returns 0.0
     45 *
     46 * @example
     47 * var v = skewness( 10, 5, 12 );
     48 * // returns NaN
     49 *
     50 * @example
     51 * var v = skewness( 10.3, 10, 4 );
     52 * // returns NaN
     53 *
     54 * @example
     55 * var v = skewness( 10, 5.5, 4 );
     56 * // returns NaN
     57 *
     58 * @example
     59 * var v = skewness( 10, 5, 4.5 );
     60 * // returns NaN
     61 *
     62 * @example
     63 * var v = skewness( NaN, 10, 4 );
     64 * // returns NaN
     65 *
     66 * @example
     67 * var v = skewness( 20, NaN, 4 );
     68 * // returns NaN
     69 *
     70 * @example
     71 * var v = skewness( 20, 10, NaN );
     72 * // returns NaN
     73 */
     74 function skewness( N, K, n ) {
     75 	var p;
     76 	var q;
     77 	if (
     78 		!isNonNegativeInteger( N ) ||
     79 		!isNonNegativeInteger( K ) ||
     80 		!isNonNegativeInteger( n ) ||
     81 		N === PINF ||
     82 		K === PINF ||
     83 		K > N ||
     84 		n > N
     85 	) {
     86 		return NaN;
     87 	}
     88 	p = ( N - (2*K) ) * sqrt( N - 1 ) * ( N - (2*n) );
     89 	q = sqrt( n * K * ( N-K ) * ( N-n ) ) * ( N - 2 );
     90 	return p / q;
     91 }
     92 
     93 
     94 // EXPORTS //
     95 
     96 module.exports = skewness;