How to resolve "Conversion to double from cell is not possible."

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James Carter 2013-5-1

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https://ww2.mathworks.cn/matlabcentral/answers/74254-how-to-resolve-conversion-to-double-from-cell-is-not-possible

评论： Walter Roberson 2018-9-27

Can someone point out what I am doing wrong. If I use the internals of the following function in command-line, the code works fine, but when I attempt to execute through the function, I get the error listed above listed for line 12. The offending code is: NewArry(3:LenB+2) = varargin;

    function [maxVal, maxInd] = inner_product(varargin)
    % varargin contains the accumulated signal returns 
    K = [2 3 10 2 1];
    LenB = length(varargin);
    EndL = varargin(1);
    EndR = varargin(LenB);
    %Pre-allocate New Array
    NewArry = zeros(1,LenB + 4);
    NewArry(3:LenB+2) = varargin;
    NewArry(1) = EndL;
    NewArry(2) = EndL;
    NewArry(LenB + 3) = EndR;
    NewArry(LenB + 4) = EndR;
    FinalArry = zeros(1:LenB); %Preallocate array to hold inner product values
    for x = 1:LenB
        %Take the first group of 5 from the NewArray
        Y = NewArry(x:x+4);
        %Take The Inner Product of this with the Kernel
        IP = Y * K';
        %Store this value
        FinalArry(1,x) = IP;
    end
    [maxVal, maxInd] = max(FinalArry);
    end

When I assign varargin, and then pass it to the function, [maxVal, maxInd] = inner_product(varargin) it fails.

Thanks

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Walter Roberson 2018-9-27

FinalArry = zeros(1:LenB);

is incorrect. It would try to create a 1 x 2 x 3 x 4 x.... LenB array.

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Answer 1

Walter Roberson 2013-5-1

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varargin is a cell array, and you cannot assign a cell array to a numeric array. Look again at your statements

NewArry = zeros(1,LenB + 4);
NewArry(3:LenB+2) = varargin;

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James Carter 2013-5-1

varargin is a 1 x 1021 vector, not a cell array, so I am not sure where it is picking up that classification. Besides, why does this work when I run the bare code outside the function but then only triggers the error when I run the exact same code within the function? Attempting to use the cell2mat routine then results in a dimensional mismatch.

Thanks

JC

Walter Roberson 2013-5-1

在 MATLAB Online 中打开

No, varargin{1} might be a 1 x 1021 vector, but varargin will always be a cell array.

Outside of a function, varargin references the script that is just the help information for varargin, and would present an error if used in a context that requires a value. varargin inside a function is special.

foo = @(varargin) class(varargin)

now try

foo([1 2 3])

and

foo('hello', 83)

and notice that each time the result is "cell".

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