Performing array operations based on logicals

[matts05]

Hi,
I'm new to FORTRAN and only have real experience in MATLAB.

What I've got is two arrays. If the elements in one array are less than a parameter, I want to perform an operation on the corresponding elements of the other array. Otherwise, I want to perform a different operation.

Since MATLAB indices can be logical arrays, this is how I would do it in MATLAB in 5 simple lines:

a = [1 3 5 7 9];
b = [0 2 4 6 8];
c = zeros(5,1);
c(a>4) = 3*b;
c(a<=4) = 2*b

This would result in
c = [0 4 12 18 24]

How would I go about doing this operation in FORTRAN? I could use an if loop nested in a do loop, but wouldn't that be inefficient? If FORTRAN does not have this similar capability to MATLAB, what would be a good algorithm to use in this case?

Thanks!

 

[xwb]

The following won't work on F77. You have to be on at least F90.

program main
integer, dimension(5):: a, b, c

! a = [1 3 5 7 9];
a = (/ 1, 3, 5, 7, 9 /)
! b = [0 2 4 6 8];
b = (/ 0, 2, 4, 6, 8 /)
! c = zeros(5,1);
c = 0

! c(a>4) = 3*b;
where (a > 4) 
   c = 3 * b
else where
! c(a<=4) = 2*b
   c = 2 * b
end where

print *, c
end