time-to-botec

README.md (5418B)

---

 <!--
 
 @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.
 
 -->
 
 # sasum
 
 > Compute the sum of [absolute values][@stdlib/math/base/special/abs] ([_L1_ norm][l1norm]).
 
 <section class="intro">
 
 The [_L1_ norm][l1norm] is defined as
 
 <!-- <equation class="equation" label="eq:l1norm" align="center" raw="\|\mathbf{x}\|_1 = \sum_{i=0}^{n-1} \vert x_i \vert" alt="L1 norm definition."> -->
 
 <div class="equation" align="center" data-raw-text="\|\mathbf{x}\|_1 = \sum_{i=0}^{n-1} \vert x_i \vert" data-equation="eq:l1norm">
     <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@c403cb0cbb15d9b7b453e3cea34ca2379500ddd4/lib/node_modules/@stdlib/blas/base/sasum/docs/img/equation_l1norm.svg" alt="L1 norm definition.">
     <br>
 </div>
 
 <!-- </equation> -->
 
 </section>
 
 <!-- /.intro -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var sasum = require( '@stdlib/blas/base/sasum' );
 ```
 
 #### sasum( N, x, stride )
 
 Computes the sum of [absolute values][@stdlib/math/base/special/abs].
 
 ```javascript
 var Float32Array = require( '@stdlib/array/float32' );
 
 var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
 
 var sum = sasum( x.length, x, 1 );
 // returns 19.0
 ```
 
 The function has the following parameters:
 
 -   **N**: number of elements to sum.
 -   **x**: input [`Float32Array`][mdn-float32array].
 -   **stride**: index increment.
 
 The `N` and `stride` parameters determine which elements in `x` are used to compute the sum. For example, to sum every other value,
 
 ```javascript
 var Float32Array = require( '@stdlib/array/float32' );
 var floor = require( '@stdlib/math/base/special/floor' );
 
 var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
 
 var N = floor( x.length / 2 );
 var stride = 2;
 
 var sum = sasum( N, x, stride );
 // returns 10.0
 ```
 
 Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
 
 ```javascript
 var Float32Array = require( '@stdlib/array/float32' );
 var floor = require( '@stdlib/math/base/special/floor' );
 
 // Initial array...
 var x0 = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
 
 // Create an offset view...
 var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
 
 var N = floor( x0.length / 2 );
 
 // Sum every other value...
 var sum = sasum( N, x1, 2 );
 // returns 12.0
 ```
 
 If either `N` or `stride` is less than or equal to `0`, the function returns `0`.
 
 #### sasum.ndarray( N, x, stride, offset )
 
 Computes the sum of [absolute values][@stdlib/math/base/special/abs] using alternative indexing semantics.
 
 ```javascript
 var Float32Array = require( '@stdlib/array/float32' );
 
 var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
 
 var sum = sasum.ndarray( x.length, x, 1, 0 );
 // returns 19.0
 ```
 
 The function has the following additional parameters:
 
 -   **offset**: starting index.
 
 While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offset` parameter supports indexing semantics based on a starting index. For example, to sum the last three elements,
 
 ```javascript
 var Float32Array = require( '@stdlib/array/float32' );
 
 var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
 
 var sum = sasum.ndarray( 3, x, 1, x.length-3 );
 // returns 15.0
 
 // Using a negative stride to sum from the last element:
 sum = sasum.ndarray( 3, x, -1, x.length-1 );
 // returns 15.0
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <section class="notes">
 
 ## Notes
 
 -   If `N <= 0`, both functions return `0`.
 -   `sasum()` corresponds to the [BLAS][blas] level 1 function [`sasum`][sasum].
 
 </section>
 
 <!-- /.notes -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var round = require( '@stdlib/math/base/special/round' );
 var randu = require( '@stdlib/random/base/randu' );
 var Float32Array = require( '@stdlib/array/float32' );
 var sasum = require( '@stdlib/blas/base/sasum' );
 
 var rand;
 var sign;
 var x;
 var i;
 
 x = new Float32Array( 100 );
 for ( i = 0; i < x.length; i++ ) {
     rand = round( randu()*100.0 );
     sign = randu();
     if ( sign < 0.5 ) {
         sign = -1.0;
     } else {
         sign = 1.0;
     }
     x[ i ] = sign * rand;
 }
 console.log( sasum( x.length, x, 1 ) );
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <section class="links">
 
 [blas]: http://www.netlib.org/blas
 
 [sasum]: http://www.netlib.org/lapack/explore-html/df/d28/group__single__blas__level1.html
 
 [mdn-float32array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array
 
 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
 
 [l1norm]: http://en.wikipedia.org/wiki/Norm_%28mathematics%29
 
 [@stdlib/math/base/special/abs]: https://www.npmjs.com/package/@stdlib/math-base-special-abs
 
 </section>
 
 <!-- /.links -->