## SUB2IND Convert Multiple Indexing To Linear Indexing

Section: Elementary Functions

### Usage

The `sub2ind` function converts a multi-dimensional indexing expression into a linear (or vector) indexing expression. The syntax for its use is
```   y = sub2ind(sizevec,d1,d2,...,dn)
```

where `sizevec` is the size of the array being indexed into, and each `di` is a vector of the same length, containing index values. The basic idea behind `sub2ind` is that it makes

```  [z(d1(1),d2(1),...,dn(1)),...,z(d1(n),d2(n),...,dn(n))]
```

equivalent to

```  z(sub2ind(size(z),d1,d2,...,dn))
```

where the later form is using vector indexing, and the former one is using native, multi-dimensional indexing.

### Example

Suppose we have a simple `3 x 4` matrix `A` containing some random integer elements
```--> A = randi(ones(3,4),10*ones(3,4))

A =
2  1  4  2
8 10  4  7
10  7  4 10
```

We can extract the elements `(1,3),(2,3),(3,4)` of `A` via `sub2ind`. To calculate which elements of `A` this corresponds to, we can use `sub2ind` as

```--> n = sub2ind(size(A),1:3,2:4)

n =
4  8 12

--> A(n)

ans =
1  4 10
```