62 lines
1.6 KiB
Markdown
62 lines
1.6 KiB
Markdown
<!-- Note: This file is automatically generated from source code comments. Changes made in this file will be overridden. -->
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# Function diag
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Create a diagonal matrix or retrieve the diagonal of a matrix
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When `x` is a vector, a matrix with vector `x` on the diagonal will be returned.
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When `x` is a two dimensional matrix, the matrixes `k`th diagonal will be returned as vector.
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When k is positive, the values are placed on the super diagonal.
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When k is negative, the values are placed on the sub diagonal.
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## Syntax
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```js
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math.diag(X)
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math.diag(X, format)
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math.diag(X, k)
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math.diag(X, k, format)
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```
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### Parameters
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Parameter | Type | Description
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--------- | ---- | -----------
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`x` | Matrix | Array | A two dimensional matrix or a vector
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`k` | number | BigNumber | The diagonal where the vector will be filled in or retrieved. Default value: 0.
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`format` | string | The matrix storage format. Default value: 'dense'.
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### Returns
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Type | Description
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---- | -----------
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Matrix | Array | Diagonal matrix from input vector, or diagonal from input matrix.
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### Throws
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Type | Description
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---- | -----------
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## Examples
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```js
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// create a diagonal matrix
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math.diag([1, 2, 3]) // returns [[1, 0, 0], [0, 2, 0], [0, 0, 3]]
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math.diag([1, 2, 3], 1) // returns [[0, 1, 0, 0], [0, 0, 2, 0], [0, 0, 0, 3]]
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math.diag([1, 2, 3], -1) // returns [[0, 0, 0], [1, 0, 0], [0, 2, 0], [0, 0, 3]]
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// retrieve the diagonal from a matrix
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const a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
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math.diag(a) // returns [1, 5, 9]
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```
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## See also
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[ones](ones.md),
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[zeros](zeros.md),
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[identity](identity.md)
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