Question

I want to sum up several vectors of different size in an array. Each time one of the vectors drops out of my program, I want to append it to my array. Like this:

array = [array, vector];

In the end I want to let this array be the output of a function. But it gives me wrong results. Is this possible with MATLAB?

Thanks and kind regards,
Damian

Answer 1

Okay, given that we’re dealing with column vectors of different size, you can’t put them all in a numerical array, since a numerical array has to be rectangular. If you really wanted to put them in the numerical array, then the column length of the array will need to be the length of the longest vector, and you’ll have to pad out the shorter vectors with NaNs.

Given this, a better solution would be, as chaohuang hinted at in the comments, to use a cell array, and store one vector in each cell. The problem is that you don’t know beforehand how many vectors there will be. The usual approach that I’m aware of for this problem is as follows (but if someone has a better idea, I’m keen to learn!):

UpperBound = SomeLargeNumber;
Array = cell(1, UpperBound);
Counter = 0;
while SomeCondition
    Counter = Counter + 1;
    if Counter > UpperBound
        error('You did not choose a large enough upper bound!');
    end
    %#Create your vector here
    Array{1, Counter} = YourVectorHere;

end
Array = Array(1, 1:Counter);

In other words, choose some upper bound beforehand that you are sure you won’t go above in the loop, and then cut your cell array down to size once the loop is finished. Also, I’ve put in an error trap in case you’re choice of upper bound turns out to be too small!

Oh, by the way, I just noted in your question the words “sum up several vectors”. Was this a figure of speech or did you actually want to perform a sum operation somewhere?