MODULE fun
  USE de_opt, ONLY : prec
CONTAINS
  REAL(KIND=prec) FUNCTION f(x)
    IMPLICIT NONE
    REAL(KIND=prec), DIMENSION(:), INTENT(IN) :: x
    REAL(KIND=prec), PARAMETER :: d = 4000.0
    INTEGER :: i, n
    REAL(KIND=prec), DIMENSION(SIZE(x)) :: ival
    n = SIZE(x)
    ival = (/ (i, i = 1, n) /)
    f = SUM((x - 100.0)**2)/d
    f = f - PRODUCT(COS((x - 100.0)/SQRT(ival))) + 1.0
  END FUNCTION f
END MODULE fun