MATLAB: Summation of Function Handle Cells

cellsfunction handleMATLABsum

Hello.

I am trying to sum up each individual cell that is produced by a function handle in a for loop that runs from.

My handle looks like this:

for a = 1 : 11;
    f{a} = @(u)1
    for b = setdiff(1:11, a); 
        f{a} = @(u)1.*G.*mass_a.*mass_b.*r./(norm_r^3)
        %need to sum up all 11 cells produced here
    end
end

The function handle spits out something like this (I have only put 2 cells, there are 11):

{@(u)1.*G.*mass_a.*mass_b.*r./(norm_r^3)}    {@(u)1.*G.*mass_a.*mass_b.*r./(norm_r^3)}

I need to sum all of the cells from above up.

It seems like the sum function on matlab does not work. I have seen a couple of instances of loops being used, but can't seem to be able to apply them correctly.

Thanks

Best Answer

fsum = @(x) sum(cellfun(@(F) F(x), f));

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MATLAB: Generating 10 samples from a binomial using a fair dice.

First, to fix your code I am guessing you are getting error messages about Xx and UR as functions or variables. To concatenate variables like you are attempting you need to put a space inbetween the variables. E.g., instead of [Xx] and [UR] use [X x] and [U R]. (But this is still not totally correct ... see second point below).

Second, you don't have a loop defined to run over the values of R ... you use R in your "if" statements like it was a scalar when in fact it is a 10 element vector. You need a loop around all of your "if-else" code and index into R inside that loop. E.g.,

R = rand(10,1) % generate a sample in Unif(0,1)
P = [1/6,2/6,3/6,4/6,5/6,1];
js = [1:6]; F = cumsum(P); disp(F)
for k=1:numel(R) % Loop over all elements of R
    if R(k) < 1/6
        x = 1;
        X = [X x];
        U = [U R(k)]; % Why are you saving R in U since you already have R?
    else if R(k) >= 1/6 && R(k) <2/6 % Note use of logical operator &&
            x = 2;
            X = [X x];
            U = [U R(k)];
(etc)
end % End of for loop

Third, there are better ways to do this that don't involve all of these if-then-else tests explicitly. Suppose instead of 6 values you needed some code that dealt with 100's of values. You would be faced with copying the if-then-else blocks 100's of times in your code to deal with all of the levels. Just as a start, you might consider what you get with the following expression:

R(k) > P

How could you use this result to come up with the x value directly without any if-then-else tests?

MATLAB: How to fill a region defined by coordinates

Mirlan - you can use fill to colour the area enclosed by your three points. For example, you can add the following to the end of your code

X = [rA(1); rB(1); rF(1)];
Y = [rA(2); rB(2); rF(2)];
fill(X, Y, 'g');

to fill the area in green.

Best Answer

Related Solutions

MATLAB: Generating 10 samples from a binomial using a fair dice.

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