time-to-botec

Benchmark sampling in different programming languages
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logpmf.js (1881B)

      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 isnan = require( '@stdlib/math/base/assert/is-nan' );
     25 var ln = require( '@stdlib/math/base/special/ln' );
     26 var NINF = require( '@stdlib/constants/float64/ninf' );
     27 
     28 
     29 // MAIN //
     30 
     31 /**
     32 * Evaluates the logarithm of the probability mass function (PMF) for a geometric distribution with success probability `p` at a value `x`.
     33 *
     34 * @param {number} x - input value
     35 * @param {Probability} p - success probability
     36 * @returns {NonPositiveNumber} logarithm of PMF
     37 *
     38 * @example
     39 * var y = logpmf( 4.0, 0.3 );
     40 * // returns ~-2.631
     41 *
     42 * @example
     43 * var y = logpmf( 2.0, 0.7 );
     44 * // returns ~-2.765
     45 *
     46 * @example
     47 * var y = logpmf( -1.0, 0.5 );
     48 * // returns -Infinity
     49 *
     50 * @example
     51 * var y = logpmf( 0.0, NaN );
     52 * // returns NaN
     53 *
     54 * @example
     55 * var y = logpmf( NaN, 0.5 );
     56 * // returns NaN
     57 *
     58 * @example
     59 * // Invalid success probability:
     60 * var y = logpmf( 2.0, 1.5 );
     61 * // returns NaN
     62 */
     63 function logpmf( x, p ) {
     64 	var q;
     65 	if ( isnan( x ) || isnan( p ) ) {
     66 		return NaN;
     67 	}
     68 	if ( p < 0.0 || p > 1.0 ) {
     69 		return NaN;
     70 	}
     71 	if ( isNonNegativeInteger( x ) ) {
     72 		q = 1.0 - p;
     73 		return ln( p ) + (x * ln( q ));
     74 	}
     75 	return NINF;
     76 }
     77 
     78 
     79 // EXPORTS //
     80 
     81 module.exports = logpmf;