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| 1 | +<!-- |
| 2 | +
|
| 3 | +@license Apache-2.0 |
| 4 | +
|
| 5 | +Copyright (c) 2018 The Stdlib Authors. |
| 6 | +
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| 7 | +Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | +you may not use this file except in compliance with the License. |
| 9 | +You may obtain a copy of the License at |
| 10 | +
|
| 11 | + http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | +
|
| 13 | +Unless required by applicable law or agreed to in writing, software |
| 14 | +distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | +See the License for the specific language governing permissions and |
| 17 | +limitations under the License. |
| 18 | +
|
| 19 | +--> |
| 20 | + |
| 21 | +# incrnanmaape |
| 22 | + |
| 23 | +> Compute the [mean arctangent absolute percentage error][@kim:2016a] (MAAPE) incrementally. |
| 24 | +
|
| 25 | +<section class="intro"> |
| 26 | + |
| 27 | +The [mean arctangent absolute percentage error][@kim:2016a] is defined as |
| 28 | + |
| 29 | +<!-- <equation class="equation" label="eq:mean_arctangent_absolute_percentage_error" align="center" raw="\operatorname{MAAPE} = \frac{1}{n} \sum_{i=0}^{n-1} \operatorname{arctan}\biggl( \biggl| \frac{a_i - f_i}{a_i} \biggr| \biggr)" alt="Equation for the mean arctangent absolute percentage error."> --> |
| 30 | + |
| 31 | +```math |
| 32 | +\mathop{\mathrm{MAAPE}} = \frac{1}{n} \sum_{i=0}^{n-1} \mathop{\mathrm{arctan}}\biggl( \biggl| \frac{a_i - f_i}{a_i} \biggr| \biggr) |
| 33 | +``` |
| 34 | + |
| 35 | +<!-- <div class="equation" align="center" data-raw-text="\operatorname{MAAPE} = \frac{1}{n} \sum_{i=0}^{n-1} \operatorname{arctan} \biggl( \biggl| \frac{a_i - f_i}{a_i} \biggr| \biggr)" data-equation="eq:mean_arctangent_absolute_percentage_error"> |
| 36 | + <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@d40d38b97af0f02f0fcc47100c3ebaca25db7c0d/lib/node_modules/@stdlib/stats/incr/maape/docs/img/equation_mean_arctangent_absolute_percentage_error.svg" alt="Equation for the mean arctangent absolute percentage error."> |
| 37 | + <br> |
| 38 | +</div> --> |
| 39 | + |
| 40 | +<!-- </equation> --> |
| 41 | + |
| 42 | +where `f_i` is the forecast value and `a_i` is the actual value. |
| 43 | + |
| 44 | +</section> |
| 45 | + |
| 46 | +<!-- /.intro --> |
| 47 | + |
| 48 | +<section class="usage"> |
| 49 | + |
| 50 | +## Usage |
| 51 | + |
| 52 | +```javascript |
| 53 | +var incrnanmaape = require( '@stdlib/stats/incr/nanmaape' ); |
| 54 | +``` |
| 55 | + |
| 56 | +#### incrnanmaape() |
| 57 | + |
| 58 | +Returns an accumulator `function` which incrementally computes the [mean arctangent absolute percentage error][@kim:2016a]. |
| 59 | + |
| 60 | +```javascript |
| 61 | +var accumulator = incrnanmaape(); |
| 62 | +``` |
| 63 | + |
| 64 | +#### accumulator( \[f, a] ) |
| 65 | + |
| 66 | +If provided input values `f` and `a`, the accumulator function returns an updated [mean arctangent absolute percentage error][@kim:2016a]. If not provided input values `f` and `a`, the accumulator function returns the current [mean arctangent absolute percentage error][@kim:2016a]. |
| 67 | + |
| 68 | +```javascript |
| 69 | +var accumulator = incrnanmaape(); |
| 70 | + |
| 71 | +var m = accumulator( 2.0, 3.0 ); |
| 72 | +// returns ~0.3218 |
| 73 | + |
| 74 | +m = accumulator( 1.0, 4.0 ); |
| 75 | +// returns ~0.4826 |
| 76 | + |
| 77 | +m = accumulator( 3.0, 5.0 ); |
| 78 | +// returns ~0.4486 |
| 79 | + |
| 80 | +m = accumulator(); |
| 81 | +// returns ~0.4486 |
| 82 | +``` |
| 83 | + |
| 84 | +</section> |
| 85 | + |
| 86 | +<!-- /.usage --> |
| 87 | + |
| 88 | +<section class="notes"> |
| 89 | + |
| 90 | +## Notes |
| 91 | + |
| 92 | +- 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. |
| 93 | +- Note that, unlike the [mean absolute percentage error][@stdlib/stats/incr/mape] (MAPE), the [mean arctangent absolute percentage error][@kim:2016a] is expressed in radians on the interval \[0,π/2]. |
| 94 | + |
| 95 | +</section> |
| 96 | + |
| 97 | +<!-- /.notes --> |
| 98 | + |
| 99 | +<section class="examples"> |
| 100 | + |
| 101 | +## Examples |
| 102 | + |
| 103 | +<!-- eslint no-undef: "error" --> |
| 104 | + |
| 105 | +```javascript |
| 106 | +var randu = require( '@stdlib/random/base/randu' ); |
| 107 | +var incrnanmaape = require( '@stdlib/stats/incr/maape' ); |
| 108 | + |
| 109 | +var accumulator; |
| 110 | +var v1; |
| 111 | +var v2; |
| 112 | +var i; |
| 113 | + |
| 114 | +// Initialize an accumulator: |
| 115 | +accumulator = incrnanmaape(); |
| 116 | + |
| 117 | +// For each simulated datum, update the mean arctangent absolute percentage error... |
| 118 | +for ( i = 0; i < 100; i++ ) { |
| 119 | + v1 = ( randu()*100.0 ) + 50.0; |
| 120 | + v2 = ( randu()*100.0 ) + 50.0; |
| 121 | + accumulator( v1, v2 ); |
| 122 | +} |
| 123 | +console.log( accumulator() ); |
| 124 | +``` |
| 125 | + |
| 126 | +</section> |
| 127 | + |
| 128 | +<!-- /.examples --> |
| 129 | + |
| 130 | +<section class="references"> |
| 131 | + |
| 132 | +## References |
| 133 | + |
| 134 | +- Kim, Sungil, and Heeyoung Kim. 2016. "A new metric of absolute percentage error for intermittent demand forecasts." _International Journal of Forecasting_ 32 (3): 669–79. doi:[10.1016/j.ijforecast.2015.12.003][@kim:2016a]. |
| 135 | + |
| 136 | +</section> |
| 137 | + |
| 138 | +<!-- /.references --> |
| 139 | + |
| 140 | +<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. --> |
| 141 | + |
| 142 | +<section class="related"> |
| 143 | + |
| 144 | +* * * |
| 145 | + |
| 146 | +## See Also |
| 147 | + |
| 148 | +- <span class="package-name">[`@stdlib/stats/incr/mae`][@stdlib/stats/incr/mae]</span><span class="delimiter">: </span><span class="description">compute the mean absolute error (MAE) incrementally.</span> |
| 149 | +- <span class="package-name">[`@stdlib/stats/incr/mape`][@stdlib/stats/incr/mape]</span><span class="delimiter">: </span><span class="description">compute the mean absolute percentage error (MAPE) incrementally.</span> |
| 150 | +- <span class="package-name">[`@stdlib/stats/incr/mean`][@stdlib/stats/incr/mean]</span><span class="delimiter">: </span><span class="description">compute an arithmetic mean incrementally.</span> |
| 151 | +- <span class="package-name">[`@stdlib/stats/incr/mmaape`][@stdlib/stats/incr/mmaape]</span><span class="delimiter">: </span><span class="description">compute a moving arctangent mean absolute percentage error (MAAPE) incrementally.</span> |
| 152 | + |
| 153 | +</section> |
| 154 | + |
| 155 | +<!-- /.related --> |
| 156 | + |
| 157 | +<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> |
| 158 | + |
| 159 | +<section class="links"> |
| 160 | + |
| 161 | +[@kim:2016a]: https://www.sciencedirect.com/science/article/pii/S0169207016000121 |
| 162 | + |
| 163 | +<!-- <related-links> --> |
| 164 | + |
| 165 | +[@stdlib/stats/incr/mae]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mae |
| 166 | + |
| 167 | +[@stdlib/stats/incr/mape]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mape |
| 168 | + |
| 169 | +[@stdlib/stats/incr/mean]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mean |
| 170 | + |
| 171 | +[@stdlib/stats/incr/mmaape]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mmaape |
| 172 | + |
| 173 | +<!-- </related-links> --> |
| 174 | + |
| 175 | +</section> |
| 176 | + |
| 177 | +<!-- /.links --> |
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