Summation of Function Handle Cells

Question

AeroLad 2020-3-30

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/514113-summation-of-function-handle-cells

评论： Omid Feizi 2021-5-23

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

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

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AeroLad 2020-3-30

编辑：AeroLad 2020-3-30

在 MATLAB Online 中打开

Hi Geoff, this is intentional. To give a bit of background, I am writing code to simulate the n-body problem.

%pp is a 11x7 struct
%Sun mass = pp(1:1, 1:1) Sun position = pp(1:1, 2:4)  Sun Velocity = pp(1:1, 5:7)
%Mercury mass = pp(2:2, 1:1) Sun position = pp(2:2, 2:4)  Sun Velocity = pp(2:2, 5:7)
%Similarly for rest of planets
[XX,No_Planets] = size(Planets)
%size = (1,11)
t0 = 0; %intital time (days)
T = 365*0.5; %final time
dt = 10; %timestep (days) 
for t = T/dt
    for a = 1 : No_Planets;
      
        disp('Planet a:'); disp(a)
        mass_a = pp(a:a,1:1);
        r_a = [pp(a:a,2:2),pp(a:a,3:3),pp(a:a,4:4)];
        v_a = [pp(a:a,5:5),pp(a:a,6:6),pp(a:a,7:7)];
        
        f{a} = @(u)1
        
   %Loop B compares all of the planets/ bodies (except a)with planet/body a
        for b = setdiff(1:No_Planets, a); 
            
            disp('Planet b:'); disp(b)
            %Positions of a planet that is not the one chosen in 'a'
            mass_b = pp(b:b,1:1);
            r_b = [pp(b:b,2:2),pp(b:b,3:3),pp(b:b,4:4)]
            v_b = [pp(b:b,5:5),pp(b:b,6:6),pp(b:b,7:7)]
            
            r =  r_b -r_a;
            r = r'
            norm_r = norm(r);
            
            f{a} = @(u)1.*G.*mass_a.*mass_b.*r./(norm_r^3)
        
            z = zeros(1,11)  %% Attempt to sum up the function handle. Probably very wrong
            for k = 1:b
                fh = @(u) fh + f(k,:)
            end
            
        end
    end
%fv =arrayfun( @(u) fk(u), [1;11] )
    end

The aim is to get equations of motion described by

.

The vectors r_a, r_b, v_a, v_b produce something like this: 1.0e+09 * [2.865 3.383 0.1924].

In the code, r =

The summation loop will then for each row basically hold 'a' (i in the formula) constant, while taking all values of b (j in the formula), then move on to the next a, and take all 10 other values of b etc...

The outermost loop (T/dt) is still a work in progress

Thanks

James Tursa 2020-3-30

编辑：James Tursa 2020-3-30

@AeroLad: My point is that the way you are currently building your function handles the radius values r_a and r_b are only snapshots of the current r_a and r_b for that iteration. I.e., all of the function handles you are building and summing are only good for one iteration of your calculations. E.g., If you are using this in an iterative integration scheme, you would be forced to completely rebuild all of your function handles from scratch at each step in the iteration process. Is that what you intend? It seems to me that building these function handles doesn't buy you anything. Just calculating the forces directly and summing them would be quicker. But I don't know the overall goal you have.

AeroLad 2020-3-30