141 lines
3.1 KiB
Markdown
141 lines
3.1 KiB
Markdown
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<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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# incrsum
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> Compute a sum incrementally.
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<section class="intro">
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The sum is defined as
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<!-- <equation class="equation" label="eq:sum" align="center" raw="s = \sum_{i=0}^{n-1} x_i" alt="Equation for the sum."> -->
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<div class="equation" align="center" data-raw-text="s = \sum_{i=0}^{n-1} x_i" data-equation="eq:sum">
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<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@49d8cabda84033d55d7b8069f19ee3dd8b8d1496/lib/node_modules/@stdlib/stats/incr/sum/docs/img/equation_sum.svg" alt="Equation for the sum.">
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<br>
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</div>
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<!-- </equation> -->
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var incrsum = require( '@stdlib/stats/incr/sum' );
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```
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#### incrsum()
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Returns an accumulator `function` which incrementally computes a sum.
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```javascript
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var accumulator = incrsum();
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```
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#### accumulator( \[x] )
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If provided an input value `x`, the accumulator function returns an updated sum. If not provided an input value `x`, the accumulator function returns the current sum.
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```javascript
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var accumulator = incrsum();
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var sum = accumulator( 2.0 );
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// returns 2.0
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sum = accumulator( 1.0 );
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// returns 3.0
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sum = accumulator( 3.0 );
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// returns 6.0
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sum = accumulator();
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// returns 6.0
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- Input values are **not** type checked. If provided `NaN` or a value which, when used in computations, results in `NaN`, the accumulated value is `NaN` for **all** future invocations. If non-numeric inputs are possible, you are advised to type check and handle accordingly **before** passing the value to the accumulator function.
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- For long running accumulations or accumulations of large numbers, care should be taken to prevent overflow.
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var randu = require( '@stdlib/random/base/randu' );
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var incrsum = require( '@stdlib/stats/incr/sum' );
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var accumulator;
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var v;
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var i;
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// Initialize an accumulator:
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accumulator = incrsum();
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// For each simulated datum, update the sum...
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for ( i = 0; i < 100; i++ ) {
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v = randu() * 100.0;
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accumulator( v );
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}
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console.log( accumulator() );
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```
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</section>
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<!-- /.examples -->
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* * *
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<section class="references">
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## References
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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][@klein:2005a].
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</section>
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<!-- /.references -->
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<section class="links">
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[@klein:2005a]: https://doi.org/10.1007/s00607-005-0139-x
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</section>
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<!-- /.links -->
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