105 lines
2.3 KiB
JavaScript
105 lines
2.3 KiB
JavaScript
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/**
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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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// MAIN //
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/**
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* Returns an accumulator function which incrementally computes a sum.
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*
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* ## Method
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*
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* - This implementation uses a second-order "iterative Kahan–Babuška algorithm", as proposed by Klein (2005).
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*
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* ## References
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*
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* - Klein, Andreas. 2005. "A Generalized Kahan-Babuška-Summation-Algorithm." _Computing_ 76 (3): 279–93. doi:[10.1007/s00607-005-0139-x](https://doi.org/10.1007/s00607-005-0139-x).
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*
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* @returns {Function} accumulator function
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*
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* @example
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* var accumulator = incrsum();
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*
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* var sum = accumulator();
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* // returns null
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*
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* sum = accumulator( 2.0 );
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* // returns 2.0
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*
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* sum = accumulator( -5.0 );
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* // returns -3.0
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*
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* sum = accumulator();
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* // returns -3.0
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*/
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function incrsum() {
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var sum;
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var ccs;
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var FLG;
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var cs;
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var cc;
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var t;
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var c;
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sum = 0.0;
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ccs = 0.0; // second order correction term for lost low order bits
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cs = 0.0; // first order correction term for lost low order bits
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return accumulator;
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/**
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* If provided a value, the accumulator function returns an updated sum. If not provided a value, the accumulator function returns the current sum.
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*
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* @private
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* @param {number} [x] - new value
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* @returns {(number|null)} sum or null
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*/
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function accumulator( x ) {
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if ( arguments.length === 0 ) {
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return ( FLG ) ? sum+cs+ccs : null;
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}
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FLG = true;
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t = sum + x;
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if ( abs( sum ) >= abs( x ) ) {
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c = (sum-t) + x;
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} else {
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c = (x-t) + sum;
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}
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sum = t;
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t = cs + c;
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if ( abs( cs ) >= abs( c ) ) {
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cc = (cs-t) + c;
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} else {
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cc = (c-t) + cs;
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}
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cs = t;
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ccs += cc;
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return sum + cs + ccs;
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}
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}
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// EXPORTS //
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module.exports = incrsum;
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