# Colon :

## Purpose

Create vectors, matrix subscripting, and `for` iterations.

## Description

The colon is one of the most useful operators in MATLAB. It can create vectors, subscript matrices, and specify `for` iterations.

The colon operator uses the following rules to create regularly spaced vectors:

```-------------------------------------------------------------------
j:k    is the same as [j,j+1,...,k]
j:k    is empty if j > k
j:i:k  is the same as [j,j+i,j+2i, ...,k]
j:i:k  is empty if i > 0 and j > k or if i < 0 and j < k
-------------------------------------------------------------------
```
Below are the definitions that govern the use of the colon to pick out selected rows, columns, and elements of vectors and matrices:

```-------------------------------------------------------------------
A(:,j)    is the j-th column of A
A(i,:)    is the i-th row of A
A(:,:)    is the same as A
A(j:k)    is A(j), A(j+1),...,A(k)
A(:,j:k)  is A(:,j), A(:,j+1),...,A(:,k)
A(:)      is all the elements of A, regarded as a single column. On
the left side of an assignment statement, A(:) fills A,
preserving its shape from before.
-------------------------------------------------------------------
```

## Examples

Using the colon with integers,

````D = 1:4`
```
results in

````D =`
`    1    2    3    4`
```
Using two colons to create a vector with arbitrary real increments between the elements,

````E = 0:.1:.5`
```
results in

````E =`
`    0    0.1000    0.2000    0.3000    0.4000    0.5000`
```

````for`, `linspace`, `logspace`, `reshape`