Correct memory access pattern section in matlab-performance-optimizer skill#15
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jamesboneham wants to merge 1 commit intomatlab:mainfrom
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Correct memory access pattern section in matlab-performance-optimizer skill#15jamesboneham wants to merge 1 commit intomatlab:mainfrom
jamesboneham wants to merge 1 commit intomatlab:mainfrom
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There is an error in the matlab-performance-optimizer skill, in this section on efficient memory access, suggesting looping first by column index `j`, and then by row index `i` is faster. This is back-to-front: if you were to generate and print `k = sub2ind([rows cols],i,j)` inside the inner loop, the first "slow" one would print the sorted flat indices (indicating contiguous memory access), whereas the "fast" one has to stride across columns.
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There is an error in the matlab-performance-optimizer skill, in this section on efficient memory access, suggesting looping first by column index
j, and then by row indexiis faster.This is back-to-front: if you were to generate and print the index into the flattened array
k = sub2ind([rows cols],i,j)inside the inner loop, the first "slow" one would print sortedk(indicating contiguous memory access), whereas the "fast" one has to stride across columns (indicating inefficient memory access).