what is the time complexity of function 'reshape'
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In reshape the actual data are not touched, but only the vector of dimension. This vector is changed, so Matlab has to allocate a new vector. The checks, if the number of elements are compatible is most likely mire expensive then allocating the vector of the new dimensions. In addition you will most likely use less than 20 dimensions. Therefore I conclude, that reshape runs in almost fixed time.
John D'Errico 2022-4-10
编辑：John D'Errico 2022-4-10
Essentially, almost zero time (a small constant amount that is almost negligable.) All reshape itself does is modify a flag attached to the array, that tells MATLAB what shape the array is. NO elements are moved around by a reshape. Of course, if you will then be doing something with that reshaped array, perhaps creating a new variable, that is different. But there, the time will be spent allocating a new variable, and copying elements, etc. But the reshape itself is virtually instantaneous.