Hello! ...

Santosh_R_ · ‎02-09-2017

Hello!

I am trying to run the following program but I am ending up with an error.

forrtl: severe (174): SIGSEGV, segmentation fault occurred
Image PC Routine Line Source
a.out 0000000000402BFA Unknown Unknown Unknown
a.out 0000000000402AAC Unknown Unknown Unknown
libc.so.6 000000341AC1ED1D Unknown Unknown Unknown
a.out 00000000004029A9 Unknown Unknown Unknown

Please help me

program roots

implicit none
real :: p,q,r, x_r1,x_r2,x_im1,x_im2
write(*,*)"please enter the values of the follwing variables"
write(*,*)"a,b,c"
read(*,*) p,q,r
call rootsfind
write(*,*) "x_real1=",x_r1,"x_real2=", x_r2
write(*,*) "x_imag1=",x_im1,"x_imag2=", x_im2
stop
end program roots

! started writing the subroutine

subroutine rootsfind(a,b,c,x_real1,x_real2,x_imag1,x_imag2,i)
implicit none
real::discr,d
real,intent(in)::a,b,c
real,intent(out)::x_real1,x_real2,x_imag1,x_imag2
integer,intent(out)::i
real,parameter::epsilon=1e-05
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
if (abs(a)<=epsilon) then
x_real1=-b/2*a;x_real2=0
x_imag1=0;x_imag2=0
i=1
return
end if

discr=b*b-4*a*c
d=sqrt(discr)

if (discr>=0)then
i=2
x_real1=(-b+d)/2*a
x_real2=(-b-d)/2*a
x_imag1=0;x_imag2=0
else
i=3
x_real1=-0.5*b/a; x_real2=x_real1
x_imag1=0.5*d/a;x_imag2=-x_imag1
end if

end subroutine rootsfind

jimdempseyatthecove · ‎02-09-2017

Your

call rootsfind

is not supplying the arguments to

subroutine rootsfind(a,b,c,x_real1,x_real2,x_imag1,x_imag2,i)

Jim Dempsey

Santosh_R_ · ‎02-09-2017

Dear Jim Dempsey,

I am new to Fortran programming Please elaborate it a bit

Thank you

Santosh R

Santosh_R_ · ‎02-09-2017

Dear Jim Dempsey,

Thank you so much I could rectify this error now.

Santosh R

jimdempseyatthecove · ‎02-10-2017

Additional information you may find of use.

In your original program, you were setting variables in the scope of the PROGRAM ROOTS, then making the call to ROOTSFIND. This is one instance of performing the method in rootsfind. Now then, assume in your PROGRAM ROOTS you want to make the call to ROOTSFIND in multiple places, each call using the same argument lists. Also assume that ROOTSFIND is never to be called from elsewhere from ROOTS. In Fortran there is a means to permit the called subroutine to have access to the namespace of the CALL-er.

**** untested code ***


program roots

       implicit none
       real :: a,b,c, x_real1,x_real2,x_imag1,x_imag2
       integer :: i
       write(*,*)"please enter the values of the follwing variables"
       write(*,*)"a,b,c"
       read(*,*) a,b,c
       call rootsfind
       write(*,*)"a,b,c", a,b,c
       write(*,*) "x_real1=",x_real1,"x_real2=", x_real2
       write(*,*) "x_imag1=",x_imag1,"x_imag2=", x_imag2
       write(*,*) "i=",i
       c = 0.0
       call rootsfind
       write(*,*)"a,b,c", a,b,c
       write(*,*) "x_real1=",x_real1,"x_real2=", x_real2
       write(*,*) "x_imag1=",x_imag1,"x_imag2=", x_imag2
       write(*,*) "i=",i
       b = 0.0
       call rootsfind
       write(*,*)"a,b,c", a,b,c
       write(*,*) "x_real1=",x_real1,"x_real2=", x_real2
       write(*,*) "x_imag1=",x_imag1,"x_imag2=", x_imag2
       write(*,*) "i=",i
       stop

       contains
       subroutine rootsfind
         implicit none
         real::discr,d
         real,parameter::epsilon=1e-05
         !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
         if (abs(a)<=epsilon) then
           x_real1=-b/2*a;x_real2=0
           x_imag1=0;x_imag2=0
           i=1
           return
         end if

         discr=b*b-4*a*c
         d=sqrt(discr)
         if (discr>=0)then
           i=2
           x_real1=(-b+d)/2*a
           x_real2=(-b-d)/2*a
           x_imag1=0;x_imag2=0
         else
           i=3
           x_real1=-0.5*b/a; x_real2=x_real1
           x_imag1=0.5*d/a;x_imag2=-x_imag1
         end if
       end subroutine rootsfind
end program roots

Jim Dempsey

Santosh_R_ · ‎02-10-2017

Dear Jim Dempsey,

Thank you ver much for your kind reply. It is very useful for beginners like me.

I will definitely be in touch with you and need your help

Thank you.

Santosh R

FortranFan · ‎02-13-2017

Santosh R. wrote:

.. I am new to Fortran programming ..

@Santosh R.,

You may want to look up these sources if you plan to delve more into Fortran: