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* @license Apache-2.0
*
* Copyright (c) 2026 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 Fcn = require( '@stdlib/function/ctor' );
var chebyshevSeries = require( './main.js' );
// MAIN //
/**
* Generates a function for evaluating a Chebyshev series.
*
* ## Notes
*
* - The compiled function uses [Clenshaw's algorithm][clenshaw-algorithm] for efficient computation.
*
* [clenshaw-algorithm]: https://en.wikipedia.org/wiki/Clenshaw_algorithm
*
* @param {NumericArray} c - Chebyshev series coefficients in descending degree order
* @returns {Function} function for evaluating a Chebyshev series
*
* @example
* var polyval = factory( [ 1.0, 0.5 ] );
*
* var v = polyval( 1.0 ); // 1*T_0(1/2) + 0.5*T_1(1/2)
* // returns 0.75
*
* var v = polyval( 0.0 ); // 1*T_0(0) + 0.5*T_1(0)
* // returns 0.25
*/
function factory( c ) {
var f;
var n;
var i;
// Use the general implementation if the number of coefficients is large:
if ( c.length > 500 ) {
return evaluate;
}
n = c.length;
// Code generation. Start with the function definition...
f = 'return function chebyshevSeries(x){';
f += 'var b0;';
f += 'var b1;';
f += 'var b2;';
// If no coefficients, the function always returns zero...
if ( n === 0 ) {
f += 'return 0.0;';
}
// If only one coefficient, the function always returns that coefficient...
else if ( n === 1 ) {
f += 'return ' + ( 0.5 * c[ 0 ] ) + ';';
}
// If more than one coefficient, apply Clenshaw's algorithm...
else {
// Initialize:
f += 'b0 = ' + c[ 0 ] + ';';
f += 'b1 = 0.0;';
// Recurrence:
for ( i = 1; i < n; i++ ) {
f += 'b2 = b1;';
f += 'b1 = b0;';
f += 'b0 = (x*b1) - b2 + ' + c[ i ] + ';';
}
f += 'return 0.5 * (b0 - b2);';
}
// Close the function:
f += '};';
// Add a source directive for debugging:
f += '//# sourceURL=chebyshevSeries.factory.js';
// Create the function in the global scope:
return ( new Fcn( f ) )();
/**
* Evaluates a Chebyshev series.
*
* @private
* @param {number} x - evaluation point
* @returns {number} evaluated series
*/
function evaluate( x ) {
return chebyshevSeries( x, c );
}
}
// EXPORTS //
module.exports = factory;
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