Il Linguaggio Fortran 90/95

56 Tipi ed espressioni
dfdx_4 = (f2_4 - f1_4)/dx_4
abs_err_4 = ABS(dfdx_exact_4 - dfdx_4)
rel_err_4 = abs_err_4/ABS(dfdx_exact_4)
! Calcola la derivata numerica per KIND=8
f2_8 = f8(x_8 + dx_8)
f1_8 = f8(x_8)
dfdx_8 = (f2_8 - f1_8)/dx_8
abs_err_8 = ABS(dfdx_exact_8 - dfdx_8)
rel_err_8 = abs_err_8/ABS(dfdx_exact_8)
! Stampa i risultati
WRITE (*,’(ES10.2,5ES11.3)’) dx_8, dfdx_exact_8, dfdx_4, &
rel_err_4, dfdx_8, rel_err_8
! Riduce il passo dx
dx_4 = dx_4*0.5_4
dx_8 = dx_8*0.5_8
IF (dx_4 < 1.0E-8) EXIT
END DO
CONTAINS
REAL(KIND=4) FUNCTION f4(x) RESULT(y)
IMPLICIT NONE
REAL(KIND=4), INTENT(IN) :: x
y = SIN(2.0_4*x)
END FUNCTION f4
!
REAL(KIND=8) FUNCTION f8(x) RESULT(y)
IMPLICIT NONE
REAL(KIND=8), INTENT(IN) :: x
y = SIN(2.0_8*x)
END FUNCTION f8
!
REAL(KIND=4) FUNCTION dfdx4(x) RESULT(dydx)
IMPLICIT NONE
REAL(KIND=4), INTENT(IN) :: x
dydx = 2*COS(2*x)
END FUNCTION dfdx4
!
REAL(KIND=8) FUNCTION dfdx8(x) RESULT(dydx)
IMPLICIT NONE
REAL(KIND=8), INTENT(IN) :: x
dydx = 2*COS(2*x)
END FUNCTION dfdx8
END PROGRAM derivate
Eseguito su un PC con processore Intel Pentium III con sistema operativo Windows 2000 il