问题
I have an array initialization based on an implied do loop, given an odd size N.
J=(N+1)/2
XLOC(1:N) = (/ (I-J, I=1,N) /)
In the context of F90+ is it recommended to use the (/ .. /) syntax, or is more efficient to use a FORALL statement.
Example: for N=19 then XLOC=(-9,-8,-7,-6,-5,-4,-3,-2,-1,0,1,2,3,4,5,6,7,8,9)
How else would you initialize this array?
Edit 1
How would you initialize this array with more readable code?
回答1:
For such a simple construct both are likely to lead to the same code because compilers are good at optimizing. The FORALL statement is not so much a looping statement but an initialization statement that has many restrictions that can inhibit optimizations. If a simple loop will work, I'd use it.
Also see this previous answer: Do Fortran 95 constructs such as WHERE, FORALL and SPREAD generally result in faster parallel code?
回答2:
There is no reason they should be less efficient that actual do loops. If you find a case, where they are, report it as an missed optimization bug to your compiler vendor!
来源：https://stackoverflow.com/questions/4563918/are-implied-do-loops-inefficient