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@stdlib/stats

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Standard library statistical functions.

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/** * @license Apache-2.0 * * Copyright (c) 2018 The Stdlib Authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ 'use strict'; // MODULES // var sqrt = require( '@stdlib/math/base/special/sqrt' ); // MAIN // /** * Returns the skewness of an F distribution. * * @param {PositiveNumber} d1 - numerator degrees of freedom * @param {PositiveNumber} d2 - denominator degrees of freedom * @returns {PositiveNumber} skewness * * @example * var v = skewness( 3.0, 7.0 ); * // returns 11.0 * * @example * var v = skewness( 4.0, 12.0 ); * // returns ~3.207 * * @example * var v = skewness( 8.0, 7.0 ); * // returns ~10.088 * * @example * var v = skewness( 1.0, 4.0 ); * // returns NaN * * @example * var v = skewness( 1.0, -0.1 ); * // returns NaN * * @example * var v = skewness( -0.1, 1.0 ); * // returns NaN * * @example * var v = skewness( 2.0, NaN ); * // returns NaN * * @example * var v = skewness( NaN, 2.0 ); * // returns NaN */ function skewness( d1, d2 ) { var out; if ( d1 <= 0.0 || d2 <= 6.0 ) { return NaN; } out = ( ( 2.0*d1 ) + d2 - 2.0 ) * sqrt( 8.0 * ( d2-4.0 ) ); out /= ( d2-6.0 ) * sqrt( d1 * ( d1+d2-2.0 ) ); return out; } // EXPORTS // module.exports = skewness;