87 lines
2.1 KiB
Markdown
87 lines
2.1 KiB
Markdown
---
|
|
title: Identity matrix
|
|
id: 5a23c84252665b21eecc7eb1
|
|
challengeType: 5
|
|
forumTopicId: 302290
|
|
---
|
|
|
|
## Description
|
|
<section id='description'>
|
|
An <i>identity matrix</i> is a square matrix of size \( n \times n \), where the diagonal elements are all <code>1</code>s (ones), and all the other elements are all <code>0</code>s (zeroes).
|
|
<ul>
|
|
<li style="list-style: none;">\(\displaystyle I_{n}=\begin{bmatrix} 1 & 0 & 0 \cr 0 & 1 & 0 \cr 0 & 0 & 1 \cr \end{bmatrix}\)</li>
|
|
</ul>
|
|
</section>
|
|
|
|
## Instructions
|
|
<section id='instructions'>
|
|
Write a function that takes a number <code>n</code> as a parameter and returns the identity matrix of order \( n \times n \).
|
|
</section>
|
|
|
|
## Tests
|
|
<section id='tests'>
|
|
|
|
```yml
|
|
tests:
|
|
- text: <code>idMatrix</code> should be a function.
|
|
testString: assert(typeof idMatrix=='function');
|
|
- text: <code>idMatrix(1)</code> should return an array.
|
|
testString: assert(Array.isArray(idMatrix(1)));
|
|
- text: <code>idMatrix(1)</code> should return <code>[ [ 1 ] ]</code>.
|
|
testString: assert.deepEqual(idMatrix(1),results[0]);
|
|
- text: <code>idMatrix(2)</code> should return <code>[ [ 1, 0 ], [ 0, 1 ] ]</code>.
|
|
testString: assert.deepEqual(idMatrix(2),results[1]);
|
|
- text: <code>idMatrix(3)</code> should return <code>[ [ 1, 0, 0 ], [ 0, 1, 0 ], [ 0, 0, 1 ] ]</code>.
|
|
testString: assert.deepEqual(idMatrix(3),results[2]);
|
|
- text: <code>idMatrix(4)</code> should return <code>[ [ 1, 0, 0, 0 ], [ 0, 1, 0, 0 ], [ 0, 0, 1, 0 ], [ 0, 0, 0, 1 ] ]</code>.
|
|
testString: assert.deepEqual(idMatrix(4),results[3]);
|
|
|
|
```
|
|
|
|
</section>
|
|
|
|
## Challenge Seed
|
|
<section id='challengeSeed'>
|
|
|
|
<div id='js-seed'>
|
|
|
|
```js
|
|
function idMatrix(n) {
|
|
// Good luck!
|
|
}
|
|
```
|
|
|
|
</div>
|
|
|
|
|
|
### After Test
|
|
<div id='js-teardown'>
|
|
|
|
```js
|
|
let results=[[ [ 1 ] ],
|
|
[ [ 1, 0 ], [ 0, 1 ] ],
|
|
[ [ 1, 0, 0 ], [ 0, 1, 0 ], [ 0, 0, 1 ] ],
|
|
[ [ 1, 0, 0, 0 ], [ 0, 1, 0, 0 ], [ 0, 0, 1, 0 ], [ 0, 0, 0, 1 ] ]]
|
|
```
|
|
|
|
</div>
|
|
|
|
</section>
|
|
|
|
## Solution
|
|
<section id='solution'>
|
|
|
|
|
|
```js
|
|
function idMatrix(n) {
|
|
return Array.apply(null, new Array(n)).map(function (x, i, xs) {
|
|
return xs.map(function (_, k) {
|
|
return i === k ? 1 : 0;
|
|
})
|
|
});
|
|
}
|
|
|
|
```
|
|
|
|
</section>
|