58 lines
1.4 KiB
JavaScript
58 lines
1.4 KiB
JavaScript
/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var abs = require( '@stdlib/math/base/special/abs' );
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var isnan = require( '@stdlib/assert/is-nan' );
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var FOURTH_PI = require( '@stdlib/constants/float64/fourth-pi' );
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var HALF_PI = require( '@stdlib/constants/float64/half-pi' );
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var cos = require( '@stdlib/math/base/special/cos' );
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// MAIN //
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/**
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* Computes the cosine kernel for a value.
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*
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* @private
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* @param {number} u - value for which we wish to calculate the cosine kernel
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* @returns {number} the value for the kernel at u
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*
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* @example
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* var u = 5;
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* var out = cosine( u );
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* // returns 0
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*/
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function cosine(u) {
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if ( isnan( u ) ) {
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return NaN;
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}
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if ( abs( u ) > 1.0 ) {
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return 0.0;
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}
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return FOURTH_PI * cos( HALF_PI * u );
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}
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// EXPORTS //
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module.exports = cosine;
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