!!!!!!!!!!!!!!!!!!!!!!!!!!! Program 2.7 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! !
! Please Note: !
! !
! (1) This computer program is written by Tao Pang in conjunction with !
! his book, "An Introduction to Computational Physics," published !
! by Cambridge University Press in 1997. !
! !
! (2) No warranties, express or implied, are made for this program. !
! !
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!
PROGRAM NEWTON
!
! This program uses the Newton method to find the root of
! f(x)=exp(x)*ln(x)-x*x=0. Copyright (c) Tao Pang 1997.
!
IMPLICIT NONE
INTEGER :: ISTEP
REAL :: A,B,DL,DX,X0,X1,F,FX,DF,DFX
!
DL = 1.0E-06
A = 1.0
B = 2.0
DX = B-A
X0 = (A+B)/2.0
ISTEP = 0
DO WHILE (ABS(DX).GT.DL)
X1 = X0-FX(X0)/DFX(X0)
DX = X1-X0
X0 = X1
ISTEP = ISTEP+1
END DO
WRITE (6,"(I4,2F16.8)") ISTEP,X0,DX
END PROGRAM NEWTON
!
FUNCTION FX(X) RESULT (F)
IMPLICIT NONE
REAL :: F
REAL, INTENT (IN) :: X
!
F = EXP(X)*ALOG(X)-X*X
END FUNCTION FX
!
FUNCTION DFX (X) RESULT (DF)
IMPLICIT NONE
REAL :: DF
REAL, INTENT (IN) :: X
!
DF = EXP(X)*(ALOG(X)+1.0/X)-2.0*X
END FUNCTION DFX