MATLAB Function Reference |

Differences and approximate derivatives

**Syntax**

**Description**

```
Y = diff(X)
```

calculates differences between adjacent elements of `X`

.

If `X`

is a vector, then `diff(X)`

returns a vector, one element shorter than `X`

, of differences between adjacent elements:

If `X`

is a matrix, then `diff(X)`

returns a matrix of row differences:

In general, `diff(X)`

returns the differences calculated along the first non-singleton (`size(X,dim) > 1`

) dimension of `X`

.

```
Y = diff(X,n)
```

applies `diff`

recursively `n`

times, resulting in the nth difference. Thus, `diff(X,2)`

is the same as `diff(diff(X))`

.

```
Y = diff(X,n,dim)
```

is the nth difference function calculated along the dimension specified by scalar `dim`

. If order `n`

equals or exceeds the length of dimension `dim`

, `diff`

returns an empty array.

**Remarks**

Since each iteration of `diff`

reduces the length of `X`

along dimension `dim`

, it is possible to specify an order `n`

sufficiently high to reduce `dim`

to a singleton (`size(X,dim) = 1`

) dimension. When this happens, `diff`

continues calculating along the next nonsingleton dimension.

**Examples**

The quantity `diff(y)./diff(x)`

is an approximate derivative.

`diff(A)`

is the first-order difference along dimension `2`

.

`diff(A,3,4)`

is the third-order difference along dimension `4`

.

**See Also**

diary | dir |

© 1994-2005 The MathWorks, Inc.