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Adding a new package to the stats/incr/* namespace: @stdlib/stats/incr/nanmprod.
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‎lib/node_modules/@stdlib/stats/incr/nanmprod/README.md‎

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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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# incrnanmprod
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> Compute a moving product incrementally.
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<section class="intro">
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For a window of size `W`, the moving product is defined as
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<!-- <equation class="equation" label="eq:moving_product" align="center" raw="\prod_{i=0}^{W-1} x_i" alt="Equation for the moving product."> -->
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```math
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\prod_{i=0}^{W-1} x_i
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```
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<!-- <div class="equation" align="center" data-raw-text="\prod_{i=0}^{W-1} x_i" data-equation="eq:moving_product">
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<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@49d8cabda84033d55d7b8069f19ee3dd8b8d1496/lib/node_modules/@stdlib/stats/incr/mprod/docs/img/equation_moving_product.svg" alt="Equation for the moving product.">
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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 incrnanmprod = require( '@stdlib/stats/incr/nanmprod' );
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```
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#### incrnanmprod
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Returns an accumulator `function` which incrementally computes a moving product. The `window` parameter defines the number of values over which to compute the moving product, ignoring `NaN` values.
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```javascript
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var accumulator = incrnanmprod( 3 );
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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 product. If not provided an input value `x`, the accumulator function returns the current product.
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```javascript
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var accumulator = incrnanmprod( 3 );
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var p = accumulator();
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// returns null
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// Fill the window...
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p = accumulator( 2.0 ); // [2.0]
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// returns 2.0
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p = accumulator( 1.0 ); // [2.0, 1.0]
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// returns 2.0
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p = accumulator( 3.0 ); // [2.0, 1.0, 3.0]
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// returns 6.0
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// Window begins sliding...
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p = accumulator( -7.0 ); // [1.0, 3.0, -7.0]
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// returns -21.0
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p = accumulator( NaN );
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// returns -21.0
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p = accumulator( -5.0 ); // [3.0, -7.0, -5.0]
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// returns 105.0
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p = accumulator();
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// returns 105.0
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```
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Under certain conditions, overflow may be transient.
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```javascript
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// Large values:
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var x = 5.0e+300;
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var y = 1.0e+300;
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// Tiny value:
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var z = 2.0e-302;
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// Initialize an accumulator:
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var accumulator = incrnanmprod( 3 );
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var p = accumulator( x );
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// returns 5.0e+300
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// Transient overflow:
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p = accumulator( y );
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// returns Infinity
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// Recover a finite result:
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p = accumulator( z );
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// returns 1.0e+299
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```
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Similarly, under certain conditions, underflow may be transient.
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```javascript
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// Tiny values:
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var x = 4.0e-302;
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var y = 9.0e-303;
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// Large value:
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var z = 2.0e+300;
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// Initialize an accumulator:
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var accumulator = incrnanmprod( 3 );
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var p = accumulator( x );
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// returns 4.0e-302
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// Transient underflow:
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p = accumulator( y );
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// returns 0.0
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// Recover a non-zero result:
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p = accumulator( z );
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// returns 7.2e-304
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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 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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- As `W` values are needed to fill the window buffer, the first `W-1` returned values are calculated from smaller sample sizes. Until the window is full, each returned value is calculated from all provided values.
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- For large accumulation windows or accumulations of either large or small numbers, care should be taken to prevent overflow and underflow. Note, however, that overflow/underflow may be transient, as the accumulator does not use a double-precision floating-point number to store an accumulated product. Instead, the accumulator splits an accumulated product into a normalized **fraction** and **exponent** and updates each component separately. Doing so guards against a loss in precision.
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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 incrnanmprod = require( '@stdlib/stats/incr/mprod' );
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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 = incrnanmprod( 5 );
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// For each simulated datum, update the moving product...
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for ( i = 0; i < 100; i++ ) {
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if ( randu() < 0.2 ) {
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v = NaN;
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} else {
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v = (randu() * 10.0) - 5.0;
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}
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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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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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* * *
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## See Also
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- <span class="package-name">[`@stdlib/stats/incr/nansum`][@stdlib/stats/incr/nansum]</span><span class="delimiter">: </span><span class="description">compute a sum incrementally, ignoring NaN values.</span>
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- <span class="package-name">[`@stdlib/stats/incr/msumprod`][@stdlib/stats/incr/msumprod]</span><span class="delimiter">: </span><span class="description">compute a moving sum of products incrementally.</span>
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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<!-- <related-links> -->
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[@stdlib/stats/incr/nansum]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/nansum
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[@stdlib/stats/incr/msumprod]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/msumprod
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/stats/incr/nanmprod/benchmark/benchmark.js‎

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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 bench = require( '@stdlib/bench' );
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var randu = require( '@stdlib/random/base/randu' );
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var pkg = require( './../package.json' ).name;
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var incrnanmprod = require( './../lib' );
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// MAIN //
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bench( pkg, function benchmark( b ) {
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var f;
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var i;
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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f = incrnanmprod( (i%5)+1 );
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if ( typeof f !== 'function' ) {
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b.fail( 'should return a function' );
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}
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}
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b.toc();
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if ( typeof f !== 'function' ) {
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b.fail( 'should return a function' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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});
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bench( pkg+'::accumulator', function benchmark( b ) {
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var acc;
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var v;
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var i;
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acc = incrnanmprod( 5 );
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = acc( randu() );
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if ( v !== v ) {
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b.fail( 'should not return NaN' );
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}
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}
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b.toc();
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if ( v !== v ) {
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b.fail( 'should not return NaN' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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});

‎lib/node_modules/@stdlib/stats/incr/nanmprod/docs/img/equation_moving_product.svg‎

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‎lib/node_modules/@stdlib/stats/incr/nanmprod/docs/repl.txt‎

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{{alias}}( W )
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Returns an accumulator function which incrementally computes a moving
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product, ignoring `NaN` values.
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The `W` parameter defines the number of values over which to compute the
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moving product.
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If provided a value, the accumulator function returns an updated moving
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product. If not provided a value or provided NaN value, the accumulator function returns the
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current moving product.
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As `W` values are needed to fill the window buffer, the first `W-1` returned
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values are calculated from smaller sample sizes. Until the window is full,
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each returned value is calculated from all provided values.
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For accumulations over large windows or accumulations of large numbers, care
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should be taken to prevent overflow. Note, however, that overflow/underflow
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may be transient, as the accumulator does not use a double-precision
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floating-point number to store an accumulated product. Instead, the
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accumulator splits an accumulated product into a normalized fraction and
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exponent and updates each component separately. Doing so guards against a
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loss in precision.
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Parameters
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----------
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W: integer
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Window size.
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Returns
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-------
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acc: Function
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Accumulator function.
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Examples
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--------
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> var accumulator = {{alias}}( 3 );
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> var p = accumulator()
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null
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> p = accumulator( 2.0 )
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2.0
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> p = accumulator( -5.0 )
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-10.0
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> p = accumulator( 3.0 )
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-30.0
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> p = accumulator( NaN )
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-30.0
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> p = accumulator( 5.0 )
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-75.0
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> p = accumulator()
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-75.0
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See Also
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--------
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