Hello, I have been working with numerical tensors. I have some tensor A where Dimensions[A]={2,2,100,100,100,100}. I want to create a tensor of the form
Dimensions[A]={2*100*100,2*100*100}. This can be done for example as Flatten[A,{{1,3,4},{2,5,6}}] or as ArrayReshape[Transpose[A,...],{2*100*100,2*100*100}] .

First of all the second option is faster than the first. After comparing with matlabs equivalent I found out that mathematica is 5-10 times slower. I would appreciate any pro tricks to speed up that calculation.