PROGRAM vecgen
!
!  This program randomly generates an N-length vector V, and then
!  places all elements of V that are <= 0.5 in the vector X, which
!  is printed.
!
   IMPLICIT NONE
   INTEGER, PARAMETER :: N=10
   INTEGER :: i, j
   DOUBLE PRECISION :: V(N), X(N)
   DOUBLE PRECISION, PARAMETER :: thresh = 0.5

   CALL RANDOM_NUMBER(V)        ! randomly generate array
!
!  Look through entire V array, and add any elements below thresh to X
!
   j = 1                         ! index in X to store into
   DO i = 1, N                   ! look through entire V array
      IF (V(i) .LE. thresh) THEN ! number is within threshold
         X(j) = V(i)             ! put new number in X
         j = j + 1               ! increment X index
      END IF
   END DO
   j = j - 1                     ! J now the number of numbers below thresh
   PRINT *, 'There were', j, ' numbers below the threshold:'
   if (j .LE. 10) PRINT *, X(:j)
END PROGRAM vecgen