# mag2db

Convert magnitude to decibels (dB)

## Syntax

``ydb = mag2db(y)``

## Description

example

````ydb = mag2db(y)` expresses in decibels (dB) the magnitude measurements specified in `y`. The relationship between magnitude and decibels is $ydb=20\ast {\mathrm{log}}_{10}\left(y\right)$```

## Examples

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For this example, consider the following SISO feedback loop where the system contains multiple gain crossover or phase crossover frequencies, which leads to multiple gain or phase margin values:

Create the transfer function.

`G = tf(20,[1 7]) * tf([1 3.2 7.2],[1 -1.2 0.8]) * tf([1 -8 400],[1 33 700]);`

Use the `allmargin` command to compute all stability margins.

`m = allmargin(G)`
```m = struct with fields: GainMargin: [0.3408 3.3920] GMFrequency: [1.9421 16.4807] PhaseMargin: 68.1178 PMFrequency: 7.0762 DelayMargin: 0.1680 DMFrequency: 7.0762 Stable: 1 ```

Note that gain margins are expressed as gain ratios and not in decibels (dB). Use `mag2db` to convert the values to dB.

`GainMargins_dB = mag2db(m.GainMargin)`
```GainMargins_dB = 1×2 -9.3510 10.6091 ```

## Input Arguments

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Input array, specified as a scalar, vector, matrix, or an array. When `y` is nonscalar, `mag2db` is an element-wise operation.

Data Types: `single` | `double`
Complex Number Support: Yes

## Output Arguments

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Magnitude measurements in decibels, returned as a scalar, vector, matrix, or an array of the same size as `y`.