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Subsections

SUM Sum Function

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

$\displaystyle y(m_1,\ldots,m_{d-1},1,m_{d+1},\ldots,m_{p}) =
\sum_{k} x(m_1,\ldots,m_{d-1},k,m_{d+1},\ldots,m_{p})
$

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 = 
  <int32>  - size: [3 3]
 
Columns 1 to 3
             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 = 
  <int32>  - size: [1 3]
 
Columns 1 to 3
             8              6              5

Next, we take the sum along the rows.

--> sum(A,2)
ans = 
  <int32>  - size: [3 1]
 
Columns 1 to 1
             9  
             6  
             4


next up previous contents
Next: MEAN Mean Function Up: Elementary Functions Previous: CUMSUM Cumulative Summation Function   Contents
Samit K. Basu 2005-03-16