Calculating a seperated sum from a vector.

Hello everybody.

A=[1,2,3,4,5,6,7,8,9,10] % not a fixed size, can be build with n*5

How can I build the sum of five numbers? I know how to do it, when the length of the vector is fixed:

a=sum(A(1:5),2)

b=sum(A(6:10),2)

Can you help me putting this operation into a for loop, so that I can do it on every size of the vector?

Tahnks.

Answer 1

[Star Strider]

If you want to sum consecutive blocks of elements, no explicit looop is necessary. You can just use the reshape (link) function, then do the summation.

N = 12;                                                                     % Create Vector Length
A = 1:N;                                                                    % Create Data
len = 5;                                                                    % Number OF Elements To Sum In Each Segment

You did not say how you wanted to handle elements that were not part of a segment equal to 5, so here are two possibilities:

mtx = reshape(A(1:len*fix(numel(A)/len)), len, []);                           % Discard Elements > Multiple Of ‘len’

or:

mtx = reshape([A(:);zeros(len*ceil(numel(A)/len)-numel(A),1)], len, []);      % Zero-Pad Elements > Multiple Of ‘len’

then the summation is simply:

s = sum(mtx);

You can put the ‘mtx’ assignments within the sum argument to create a single line of code. I created ‘mtx’ separately for convenience here.