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