/**
* @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 abs = require( '@stdlib/math/base/special/abs' );
var isnan = require( '@stdlib/assert/is-nan' );
var pow = require( '@stdlib/math/base/special/pow' );


// MAIN //

/**
* Computes the Triweight kernel for a value.
*
* @private
* @param {number} u - value for which we wish to calculate the Triweight kernel
* @returns {number} the value for the kernel at u
*
* @example
* var u = 5;
* out = triweight(u); // returns 0
*/
function triweight(u) {
	var absU;

	if (isnan(u)) {
		return NaN;
	}

	absU = abs(u);
	if (absU > 1) {
		return 0;
	}
	return (35 / 32) * pow(1.0 - pow(u, 2.0), 3.0);
}


// EXPORTS //

module.exports = triweight;