## STD Standard Deviation Function

Section: Elementary Functions

### Usage

Computes the standard deviation of an array along a given dimension. The general syntax for its use is
```  y = std(x,d)
```

where `x` is an `n`-dimensions array of numerical type. The output is of the same numerical type as the input. The argument `d` is optional, and denotes the dimension along which to take the variance. The output `y` is the same size as `x`, except that it is singular along the mean direction. So, for example, if `x` is a `3 x 3 x 4` array, and we compute the mean along dimension `d=2`, then the output is of size `3 x 1 x 4`.

### Example

The following piece of code demonstrates various uses of the `std` function
```--> A = [5,1,3;3,2,1;0,3,1]

A =
5 1 3
3 2 1
0 3 1
```

We start by calling `std` without a dimension argument, in which case it defaults to the first nonsingular dimension (in this case, along the columns or `d = 1`).

```--> std(A)

ans =
2.5166    1.0000    1.1547
```

Next, we take the variance along the rows.

```--> std(A,2)

ans =
2.0000
1.0000
1.5275
```