time-to-botec

Benchmark sampling in different programming languages
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factory.js (2105B)

      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 constantFunction = require( '@stdlib/utils/constant-function' );
     24 var isnan = require( '@stdlib/math/base/assert/is-nan' );
     25 
     26 
     27 // MAIN //
     28 
     29 /**
     30 * Returns a function for evaluating the probability density function (PDF) for a triangular distribution with lower limit `a` and upper limit `b` and mode `c`.
     31 *
     32 * @param {number} a - lower limit
     33 * @param {number} b - upper limit
     34 * @param {number} c - mode
     35 * @returns {Function} PDF
     36 *
     37 * @example
     38 * var pdf = factory( 0.0, 10.0, 5.0 );
     39 * var y = pdf( 2.0 );
     40 * // returns 0.08
     41 *
     42 * y = pdf( 12.0 );
     43 * // returns 0.0
     44 */
     45 function factory( a, b, c ) {
     46 	var denom1;
     47 	var denom2;
     48 	var denom3;
     49 
     50 	if (
     51 		isnan( a ) ||
     52 		isnan( b ) ||
     53 		isnan( c ) ||
     54 		a > c ||
     55 		c > b
     56 	) {
     57 		return constantFunction( NaN );
     58 	}
     59 
     60 	denom1 = ( b - a ) * ( c - a );
     61 	denom2 = b - a;
     62 	denom3 = ( b - a ) * ( b - c );
     63 	return pdf;
     64 
     65 	/**
     66 	* Evaluates the probability density function (PDF) for a triangular distribution.
     67 	*
     68 	* @private
     69 	* @param {number} x - input value
     70 	* @returns {number} evaluated PDF
     71 	*
     72 	* @example
     73 	* var y = pdf( 12.0 );
     74 	* // returns <number>
     75 	*/
     76 	function pdf( x ) {
     77 		if ( isnan( x ) ) {
     78 			return NaN;
     79 		}
     80 		if ( x < a ) {
     81 			return 0.0;
     82 		}
     83 		// Case: x >= a
     84 		if ( x < c ) {
     85 			return 2.0 * ( x - a ) / denom1;
     86 		}
     87 		if ( x === c ) {
     88 			return 2.0 / denom2;
     89 		}
     90 		// Case: x > c
     91 		if ( x <= b ) {
     92 			return 2.0 * ( b - x ) / denom3;
     93 		}
     94 		// Case: x > b
     95 		return 0.0;
     96 	}
     97 }
     98 
     99 
    100 // EXPORTS //
    101 
    102 module.exports = factory;