# Documentation

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# wkeep

Keep part of vector or matrix

## Syntax

```Y = wkeep(X,L,OPT) Y = wkeep(X,L,FIRST) Y = wkeep(X,L) Y = wkeep(X,L,'c') Y = wkeep(X,S,[FIRSTR FIRSTC]) ```

## Description

`wkeep` is a general utility.

For a vector, `Y = wkeep(X,L,OPT)` extracts the vector `Y` from the vector `X`. The length of `Y` is `L`.

If `OPT` is equal to `'c'`, `'l'`, or `'r'`, `Y` is the central, left, or right part of `X`.

`Y = wkeep(X,L,FIRST)` returns the vector `X(FIRST:FIRST+L-1)`.

`Y = wkeep(X,L)` is equivalent to ```Y = wkeep(X,L,'c')```.

For a matrix, `Y = wkeep(X,S)` extracts the central part of the matrix `X`. The size of `Y` is `S`.

`Y = wkeep(X,S,[FIRSTR FIRSTC])` extracts the submatrix of matrix `X`, of size `S` and starting from `X(FIRSTR,FIRSTC)`.

## Examples

```% For a vector. x = 1:10; y = wkeep(x,6,'c') y = 3 4 5 6 7 8 y = wkeep(x,6) y = 3 4 5 6 7 8 y = wkeep(x,7,'c') y = 2 3 4 5 6 7 8 y = wkeep(x,6,'l') y = 1 2 3 4 5 6 y = wkeep(x,6,'r') y = 5 6 7 8 9 10 % For a matrix. x = magic(5) x = 17 24 1 8 15 23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9 y = wkeep(x,[3 2]) y = 5 7 6 13 12 19 ```