I store matrix entries in std::vector<double>, such that the reading is row by row.

This means, for matrix

1 3 4 8 9 3

3 6 8 1 1 2

2 0 9 8 7 6

the std::vector<double> would have entries: {1,3,4,8,9,3,3,6,8,1,1,2,2,0,9,8,7,6}.

To transpose the matrix I use the naive approach of iterating through std::vector, calculating for each

entry its position in a matrix transpose. Recently, I got one suggestion:

"When you have a matrix and a mapping to a one-dimensional vector, transposing is equivalent to a permutation. Now execute this permutation by sorting the elements by requested rank in the permutation result."

I understand that transposing is equivalent to a permutation, but I dont know how to approach the problem this way.

Any suggestion on how to do this (or to do matrix transpose is a faster way) is welcome.