diff Difference and discrete derivative

## Syntax

                y = diff(x)
                y = diff(x, n)
                y = diff(x, n, dim)

## Arguments

x

  vector or matrix (real, complex, sparse or polynomial)

n

  integer the order of differentiation

dim

  integer or character string with values "r","c" and "*"

y

  scalar or vector/matrix

## Description

`y=diff(x)` compute the difference function `y=x(2:$)-x(1:$-1)`

`diff(x,n,dim)` is the `n`th difference function along dimension `dim`.

`diff(x,n,"*")` is equivalent to `diff(x(:),n)`.

Default value for `n` is 1. Default value for `dim` is `"*"`.

`dim='r'` is equivalent to `dim=1` and `dim='c'` is equivalent to `dim=2`.

## Examples

    v = (1:8)^3;
    diff(v)
    diff(v,3)

    A=[(1:8)^2
       (1:8)^3
       (1:8)^4];

    diff(A,3,2)

    // approximate differentiation
    step = 0.001
    t = 0:step:10;
    y = sin(t);
    dy = diff(sin(t)) / step; //approximate differentiation of sine function
    norm(dy-cos(t(1:$-1)), %inf)

## See also

- interp
- interp2d
- splin
- eval_cshep2d
- numderivative
- sgolaydiff