All files / dists/geometric/cdf/lib main.js

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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 isnan = require( '@stdlib/math/base/assert/is-nan' );
var floor = require( '@stdlib/math/base/special/floor' );
var pow = require( '@stdlib/math/base/special/pow' );
var PINF = require( '@stdlib/constants/float64/pinf' );
 
 
// MAIN //
 
/**
* Evaluates the cumulative distribution function (CDF) for a geometric distribution with success probability `p` at a value `x`.
*
* @param {number} x - input value
* @param {Probability} p - success probability
* @returns {Probability} evaluated CDF
*
* @example
* var y = cdf( 2.0, 0.5 );
* // returns 0.875
*
* @example
* var y = cdf( 2.0, 0.1 );
* // returns ~0.271
*
* @example
* var y = cdf( -1.0, 0.5 );
* // returns 0.0
*
* @example
* var y = cdf( NaN, 0.5 );
* // returns NaN
*
* @example
* var y = cdf( 0.0, NaN );
* // returns NaN
*
* @example
* // Invalid probability
* var y = cdf( 2.0, 1.4 );
* // returns NaN
*/
function cdf( x, p ) {
	if (
		isnan( x ) ||
		isnan( p ) ||
		p < 0.0 ||
		p > 1.0
	) {
		return NaN;
	}
	if ( x < 0.0 ) {
		return 0.0;
	}
	if ( x === PINF ) {
		return 1.0;
	}
	x = floor( x );
	return 1.0 - pow( 1.0 - p, x + 1.0 );
}
 
 
// EXPORTS //
 
module.exports = cdf;