Il Linguaggio Fortran 90/95

5.7 Interfacce esplicite ed implicite 243
IMPLICIT NONE
INTEGER, PARAMETER :: dp = KIND(1D0)
REAL(KIND=dp), INTENT(INOUT) :: x
REAL(KIND=dp), INTENT(IN) :: eps
REAL(KIND=dp), EXTERNAL :: f, df
INTEGER, INTENT(IN) :: nmax
END SUBROUTINE newton
END INTERFACE
eps = 1.0E-6_dp
nmax = 100
x = 4.0_dp
CALL newton(f,df,x,nmax,eps)
END PROGRAM main
SUBROUTINE newton(f,df,x,nmax,eps)
! Scopo: applica l’algoritmo di Newton-Raphson per la valutazione
! dello zero di una funzione reale di una variabile reale
IMPLICIT NONE
INTEGER, PARAMETER :: dp=KIND(1D0)
REAL(KIND=dp), INTENT(INOUT) :: x
REAL(KIND=dp), INTENT(IN) :: eps
REAL(KIND=dp), external :: f, df
INTEGER, INTENT(IN) :: nmax
REAL(KIND=dp) :: fx
INTEGER :: n=0
WRITE(UNIT=*,FMT=’(1X,"n",12X,"x",19X,"f(x)",/,46("="))’)
fx = f(x)
WRITE(UNIT=*,FMT="(1X,I2,1X,F20.16,1X,F20.16)") n, x, fx
DO n = 1,nmax
x = x - fx/df(x)
fx = f(x)
WRITE(UNIT=*,FMT="(1X,I2,1X,F20.16,1X,F20.16)") n, x, fx
IF(ABS(fx)