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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 abs = require( '@stdlib/math/base/special/abs' );
var EPS = require( '@stdlib/constants/float64/eps' );
// VARIABLES //
var MAX_TERMS = 1000000;
// MAIN //
/**
* Sum the elements of the series given by the supplied function.
*
* @param {Function} generator - series function
* @param {Object} [options] - function options
* @param {PositiveInteger} [options.maxTerms=1000000] - maximum number of terms to be added
* @param {PositiveNumber} [options.tolerance=2.22e-16] - further terms are only added as long as the next term is greater than current term times the tolerance
* @param {number} [options.initialValue=0] - initial value of the resulting sum
* @returns {number} sum of all series terms
*
* @example
* var gen = geometricSeriesGenerator( 0.9 );
* var out = sumSeries( gen );
* // returns 10.0
*
* function* geometricSeriesGenerator( x ) {
* var exponent = 0;
* while ( true ) {
* yield Math.pow( x, exponent );
* exponent += 1;
* }
* }
*/
function sumSeries( generator, options ) {
var isgenerator;
var tolerance;
var nextTerm;
var counter;
var result;
var opts;
opts = {};
if ( arguments.length > 1 ) {
opts = options;
}
tolerance = opts.tolerance || EPS;
counter = opts.maxTerms || MAX_TERMS;
result = opts.initialValue || 0;
isgenerator = typeof generator.next === 'function';
if ( isgenerator === true ) {
// Case A: Iterate over generator object created by a generator function...
for ( nextTerm of generator ) {
result += nextTerm;
if (
abs(tolerance * result) >= abs(nextTerm) ||
--counter === 0 // eslint-disable-line no-plusplus
) {
break;
}
}
} else {
// Case B: Repeatedly call function...
do {
nextTerm = generator();
result += nextTerm;
}
while ( ( abs(tolerance * result) < abs(nextTerm) ) && --counter ); // eslint-disable-line no-plusplus
}
return result;
}
// EXPORTS //
module.exports = sumSeries;
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