SUM Sum Function

Section: Elementary Functions

Usage

Computes the summation of an array along a given dimension. The general syntax for its use is 
  y = sum(x,d)

where x is an n-dimensions array of numerical type. The output is of the same numerical type as the input. The argument d is optional, and denotes the dimension along which to take the summation. The output y is the same size as x, except that it is singular along the summation direction. So, for example, if x is a 3 x 3 x 4 array, and we compute the summation along dimension d=2, then the output is of size 3 x 1 x 4.

Function Internals

The output is computed via

If d is omitted, then the summation is taken along the first non-singleton dimension of x.

Example

The following piece of code demonstrates various uses of the summation function 
--> A = [5,1,3;3,2,1;0,3,1]

A = 
 5 1 3 
 3 2 1 
 0 3 1

We start by calling sum without a dimension argument, in which case it defaults to the first nonsingular dimension (in this case, along the columns or d = 1). 

--> sum(A)

ans = 
 8 6 5

Next, we take the sum along the rows. 

--> sum(A,2)

ans = 
 9 
 6 
 4