E:/turkuaz/krylov/codes/newton/1.2b/newton/modules/myFunctions.f90

Go to the documentation of this file.

module myFunctions

implicit none   ! implicit none's are not needed in the contained functions 
                                ! and subroutines however if one needs to copy the function
                                ! as a stand-alone code then implicit none should be present

contains


!#################################################################################
function cubic(df0,f0,fprev1,fprev2,lambdaprev1,lambdaprev2) !<cubic backtracking
implicit none
real(8) df0,f0,fprev1,fprev2,lambdaprev1,lambdaprev2
real(8) cubic,lambda
real(8) constant,BS(2,2),C(2,1),D(2,1)   ! 'A' is changed to 'constant','B' is changed to 'BS'
real(8) a,b
cubic=0.d0
lambda=0.d0
constant=1.d0/(lambdaprev1-lambdaprev2)
BS(1,1)= 1.d0/lambdaprev1**2.d0
BS(1,2)=-1.d0/lambdaprev2**2.d0
BS(2,1)=-lambdaprev2/lambdaprev1**2.d0
BS(2,2)= lambdaprev1/lambdaprev2**2.d0
C(1,1)=fprev1-f0-df0*lambdaprev1
C(2,1)=fprev2-f0-df0*lambdaprev2
D=constant*matmul(BS,C)
a=D(1,1)
b=D(2,1)
lambda=(-b+dsqrt(b**2.d0-3.d0*a*df0))/(3.d0*a)
cubic=lambda
end function
!#################################################################################
function machineps()
!<this function is equivalent to epsilon(0.d0) epsilon being a built-in function
implicit none
real(8) machineps
machineps=1.d0
do 
        machineps=machineps/2.d0
        if ((1.d0+machineps).EQ.1.d0) exit
end do
machineps=machineps*2.d0
end function machineps
!#################################################################################
function quadratic(df0,f0,f1) !<quadratic backtracking
implicit none
real(8) df0,f0,f1
real(8) quadratic,lambda
quadratic=0.d0
lambda=0.d0
lambda=-0.5d0*df0/(f1-f0-df0)
quadratic=lambda
end function
!#################################################################################







end module myFunctions

---