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feat: add stats/incr/nanmmean
PR-URL: #6185 Closes: #5588 Co-authored-by: Philipp Burckhardt <pburckhardt@outlook.com> Reviewed-by: Philipp Burckhardt <pburckhardt@outlook.com>
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<!--
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@license Apache-2.0
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Copyright (c) 2026 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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# incrnanmmean
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> Compute a moving [arithmetic mean][arithmetic-mean] incrementally, ignoring `NaN` values.
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<section class="intro">
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For a window of size `W`, the [arithmetic mean][arithmetic-mean] is defined as
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<!-- <equation class="equation" label="eq:arithmetic_mean" align="center" raw="\bar{x} = \frac{1}{W} \sum_{i=0}^{W-1} x_i" alt="Equation for the arithmetic mean."> -->
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```math
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\bar{x} = \frac{1}{W} \sum_{i=0}^{W-1} x_i
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```
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<!-- <div class="equation" align="center" data-raw-text="\bar{x} = \frac{1}{W} \sum_{i=0}^{W-1} x_i" data-equation="eq:arithmetic_mean">
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<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@320a89534d4f59b82d162f31e968222555dae2f7/lib/node_modules/@stdlib/stats/incr/nanmmean/docs/img/equation_arithmetic_mean.svg" alt="Equation for the arithmetic mean.">
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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 incrnanmmean = require( '@stdlib/stats/incr/nanmmean' );
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```
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#### incrnanmmean( window )
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Returns an accumulator `function` which incrementally computes a moving [arithmetic mean][arithmetic-mean], ignoring `NaN` values. The `window` parameter defines the number of values over which to compute the moving mean.
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```javascript
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var accumulator = incrnanmmean( 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 mean. If not provided an input value `x`, the accumulator function returns the current mean.
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```javascript
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var accumulator = incrnanmmean( 3 );
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var mu = accumulator();
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// returns null
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// Fill the window...
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mu = accumulator( 2.0 ); // [2.0]
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// returns 2.0
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mu = accumulator( 1.0 ); // [2.0, 1.0]
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// returns 1.5
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mu = accumulator( 3.0 ); // [2.0, 1.0, 3.0]
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// returns 2.0
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// Window begins sliding...
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mu = accumulator( -7.0 ); // [1.0, 3.0, -7.0]
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// returns -1.0
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mu = accumulator( NaN ); // [1.0, 3.0, -7.0]
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// returns -1.0
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mu = accumulator( -5.0 ); // [3.0, -7.0, -5.0]
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// returns -3.0
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mu = accumulator();
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// returns -3.0
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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 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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</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 uniform = require( '@stdlib/random/base/uniform' );
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var bernoulli = require( '@stdlib/random/base/bernoulli' );
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var incrnanmmean = require( '@stdlib/stats/incr/nanmmean' );
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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 = incrnanmmean( 5 );
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// For each simulated datum, update the moving mean...
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for ( i = 0; i < 100; i++ ) {
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v = ( bernoulli( 0.8 ) < 1 ) ? NaN : uniform( 0.0, 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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<!-- 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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</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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[arithmetic-mean]: https://en.wikipedia.org/wiki/Arithmetic_mean
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<!-- <related-links> -->
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<!-- </related-links> -->
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</section>
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<!-- /.links -->
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2026 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 format = require( '@stdlib/string/format' );
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var pkg = require( './../package.json' ).name;
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var incrnanmmean = 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 = incrnanmmean( (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( format( '%s::accumulator', pkg ), 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 = incrnanmmean( 5 );
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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v = acc( i );
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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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});
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{{alias}}( W )
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Returns an accumulator function which incrementally computes a moving
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arithmetic mean, 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 mean.
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If provided a value, the accumulator function returns an updated moving
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mean. If not provided a value, the accumulator function returns the current
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moving mean.
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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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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 mu = accumulator()
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null
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> mu = accumulator( 2.0 )
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2.0
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> mu = accumulator( -5.0 )
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-1.5
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> mu = accumulator( NaN )
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-1.5
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> mu = accumulator( 3.0 )
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0.0
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> mu = accumulator( 5.0 )
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1.0
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> mu = accumulator( NaN )
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1.0
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> mu = accumulator()
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1.0
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See Also
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--------
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