How to use Prod function with cell arrays

I have defined a cell array in the name of "T_mn" having "n_layers" number of cells.

Each cell is having a vector containing "n_modes" elements.

I want to find the product of element "req_mode" in each vector among the cells between "wire_lay" - "obs_lay"

when I though of using this code it is not working

for wire_lay=1:1:n_layers
     for req_mode=1:1:l_modes
         for obs_lay=1:1:n_layers
A=prod(T_mn{wire_lay:1:obs_lay}(req_mode))
end
end
end

Can you help?

Answer 1

[Adam Danz]

% Extract the value in index "req_mode" from each cell in "T_mn"
% starting and ending at cell index "wire_lay" and "obs_lay" respectively. 
wire_lay = 2; 
obs_lay = 4; 
req_mode = 3; 
vec = cellfun(@(x)x(req_mode),T_mn(wire_lay:obs_lay)); 
prd = prod(vec); 

% DEMO data 
T_mn{1} = [1 2 3 4]; 
T_mn{2} = [5 6 7 8]; 
T_mn{3} = [9 10 11 12]; 
T_mn{4} = [13 14 15 16]; 
T_mn{5} = [0 0 0 0 ]; 

[Vinay Killamsetty]

Thank you very much

Answer 2

[Rik]

It is always good to consider if the task you want to accomplish asks for a different data design. I think it is much easier to do what you want (and optimize by removing the loops) if you first convert your cell array to doubles.

Note that with this order of loops and this data design, you can replace the req_mode loop by specifying the dimension in your call to prod (A=prod(T(:,wire_lay:obs_lay),2)).

Also, the cumprod function could be helpful in optimizing this code.

% DEMO data 
T_mn{1} = [1 2 3 4]; 
T_mn{2} = [5 6 7 8]; 
T_mn{3} = [9 10 11 12]; 
T_mn{4} = [13 14 15 16]; 
T_mn{5} = [0 0 0 0 ]; 
n_layers=5;
n_modes=4;

T=squeeze(cat(3,T_mn{:}));
%cell2mat also works, but only if T_mn is 1-by-n and T_mn{} is m-by-1

for wire_lay=1:n_layers
    for req_mode=1:n_modes
        for obs_lay=wire_lay:n_layers
            A=prod(T(req_mode,wire_lay:obs_lay));
            %do something with A, otherwise it will get overwritten
        end
    end
end

[Vinay Killamsetty]

Thank you very much