feat: add ndarray/base/to-rotl90

PR-URL: #11776
Reviewed-by: Athan Reines <kgryte@gmail.com>
Closes: stdlib-js/metr-issue-tracker#305

Author: headlessNode

lib/node_modules/@stdlib/ndarray/base/to-rotl90/README.md

@@ -0,0 +1,152 @@
+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2026 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.
+
+-->
+
+# toRotl90
+
+> Return a new ndarray where a matrix (or a stack of matrices) is rotated 90 degrees counterclockwise.
+
+<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<!-- Package usage documentation. -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var toRotl90 = require( '@stdlib/ndarray/base/to-rotl90' );
+```
+
+#### toRotl90( x, k )
+
+Returns a new ndarray where a matrix (or a stack of matrices) is rotated 90 degrees counterclockwise.
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+
+var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
+// returns <ndarray>[ [ 1, 2 ], [ 3, 4 ] ]
+
+var y = toRotl90( x, 1 );
+// returns <ndarray>[ [ 2, 4 ], [ 1, 3 ] ]
+```
+
+The function accepts the following arguments:
+
+-   **x**: input ndarray.
+-   **k**: number of times to rotate by 90 degrees. Positive values rotate counterclockwise. Negative values rotate clockwise.
+
+</section>
+
+<!-- /.usage -->
+
+<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="notes">
+
+## Notes
+
+-   If `k > 0`, the function rotates the matrix counterclockwise.
+-   If `k < 0`, the function rotates the matrix clockwise.
+-   If provided an ndarray with fewer than two dimensions, the function does not perform a rotation and simply returns a copy of the input ndarray.
+
+</section>
+
+<!-- /.notes -->
+
+<!-- Package usage examples. -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var array = require( '@stdlib/ndarray/array' );
+var ndarray2array = require( '@stdlib/ndarray/to-array' );
+var toRotl90 = require( '@stdlib/ndarray/base/to-rotl90' );
+
+// Create a 2x3 matrix:
+var x = array( [ [ 1, 2, 3 ], [ 4, 5, 6 ] ] );
+
+// Rotate 90 degrees counterclockwise:
+var y = toRotl90( x, 1 );
+var arr = ndarray2array( y );
+// returns [ [ 3, 6 ], [ 2, 5 ], [ 1, 4 ] ]
+
+// Rotate 180 degrees:
+y = toRotl90( x, 2 );
+arr = ndarray2array( y );
+// returns [ [ 6, 5, 4 ], [ 3, 2, 1 ] ]
+
+// Rotate 270 degrees counterclockwise (equivalent to 90 degrees clockwise):
+y = toRotl90( x, 3 );
+arr = ndarray2array( y );
+// returns [ [ 4, 1 ], [ 5, 2 ], [ 6, 3 ] ]
+
+// Rotate 360 degrees (equivalent to no rotation):
+y = toRotl90( x, 4 );
+arr = ndarray2array( y );
+// returns [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
+
+// Rotate 90 degrees clockwise (equivalent to k=3):
+y = toRotl90( x, -1 );
+arr = ndarray2array( y );
+// returns [ [ 4, 1 ], [ 5, 2 ], [ 6, 3 ] ]
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="references">
+
+</section>
+
+<!-- /.references -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+<!-- <related-links> -->
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->