Keep part of vector or matrix

`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])

`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)`

.

% 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

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