vector.size() pull out of loop
pass by reference

slower !?
Revert "pass by reference"

This reverts commit 494b1693fd237d9ae38f940369e0c5f480d34988.
Revert "Revert "pass by reference""

This reverts commit bcd7c1981a8470d6eb5d793691a97f21f4b954ad.
Revert "pass by reference"

This reverts commit 494b1693fd237d9ae38f940369e0c5f480d34988.
test
test
omp for change private variable
omp for private var
omp for private var