Error using reshape Number of elements must not change. Use [] as one of the size inputs to automatically calculate the appropriate size for that dimension.

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Emilia Butters 2022-3-1

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https://ww2.mathworks.cn/matlabcentral/answers/1661290-error-using-reshape-number-of-elements-must-not-change-use-as-one-of-the-size-inputs-to-automati

评论： Walter Roberson 2022-3-2

Hi,

I have the following code inside of a function:

x = exp(xi);
sz = size(x, 1)-255;
a = reshape(x(1:sz-1,:), [255 256]); 
b = x(sz:end, :);

I am using a minimisation function on this function which throws the following error.

Error using reshape
Number of elements must not change. Use [] as one of the size inputs to automatically calculate the appropriate
size for that dimension.
Error in minimize (line 75)
[f0 df0] = feval(f, X, varargin{:});          % get function value and gradient

I would appreciate any ideas as to why this error might be occuring. Thanks! :)

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Answer 1

Walter Roberson 2022-3-1

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https://ww2.mathworks.cn/matlabcentral/answers/1661290-error-using-reshape-number-of-elements-must-not-change-use-as-one-of-the-size-inputs-to-automati#answer_907335

在 MATLAB Online 中打开

sz = size(x, 1)-255;
a = reshape(x(1:sz-1,:), [255 256]); 

So x(1:sz-1,:) would get all except the last 256 rows of x . And then you reshape that to 255 by 256. that is only going to work if the original data was 511 x 256 or certain other "magic" size combinations.

The reason to use things like size(x,1) are to permit flexibility in the size of the array x. But your reshape() is coded in a way that provides no flexibility: it demands that the data be exactly a certain number of elements, which contradicts the request for general size handling gained by asking size()

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Emilia Butters 2022-3-1

在 MATLAB Online 中打开

Ah okay thanks! I've fixed it to the following but it still throws the reshape error...

theta_unlog = exp(theta);
sz = size(theta_unlog, 1);
new_sz = sz-256;
new_theta = theta_unlog(1:new_sz,:); 
a = reshape(new_theta, [255 256]); 
b = theta_unlog(new_sz+1:end, :);

Walter Roberson 2022-3-2

If you want the remaining to have 255*256 elements after you took away 256 then it follows that the original should have 255*256 + 1*256 = 256*256 elements, which is 65536

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Error using reshape Number of elements must not change. Use [] as one of the size inputs to automatically calculate the appropriate size for that dimension.

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Error using reshape Number of elements must not change. Use [] as one of the size inputs to automatically calculate the appropriate size for that dimension.

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