Press n or j to go to the next uncovered block, b, p or k for the previous block.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 | 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x | /**
* @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 constantFunction = require( '@stdlib/utils/constant-function' );
var degenerate = require( '@stdlib/stats/base/dists/degenerate/logpdf' ).factory;
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var gammaln = require( '@stdlib/math/base/special/gammaln' );
var ln = require( '@stdlib/math/base/special/ln' );
var NINF = require( '@stdlib/constants/float64/ninf' );
var PINF = require( '@stdlib/constants/float64/pinf' );
var LN2 = require( '@stdlib/constants/float64/ln-two' );
// MAIN //
/**
* Returns a function for evaluating the natural logarithm of the probability density function (PDF) for a chi distribution with degrees of freedom `k`.
*
* @param {NonNegativeNumber} k - degrees of freedom
* @returns {Function} logPDF
*
* @example
* var logpdf = factory( 0.5 );
*
* var y = logpdf( 2.0 );
* // returns ~-3.115
*
* y = logpdf( 1.0 );
* // returns ~-1.268
*/
function factory( k ) {
var km1;
var kh;
if ( isnan( k ) || k < 0.0 ) {
return constantFunction( NaN );
}
if ( k === 0.0 ) {
return degenerate( 0.0 );
}
kh = k / 2.0;
km1 = k - 1.0;
return logpdf;
/**
* Evaluates the natural logarithm of the probability density function (PDF) for a chi distribution with degrees of freedom `k`.
*
* @private
* @param {number} x - input value
* @returns {number} evaluated logPDF
*
* @example
* var y = logpdf( 1.0 );
* // returns <number>
*/
function logpdf( x ) {
var out;
if ( isnan( x ) ) {
return NaN;
}
if ( x < 0.0 || x === PINF ) {
return NINF;
}
out = ( ( 1.0-kh ) * LN2 ) + ( km1 * ln( x ) ) - ( (x*x) / 2.0 );
out -= gammaln( kh );
return out;
}
}
// EXPORTS //
module.exports = factory;
|