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Hello! ...

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

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6 Replies
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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

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Beginner
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Dear Jim Dempsey,

 

I am new to Fortran programming Please elaborate it a bit 

 

Thank you

Santosh R

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Beginner
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Dear Jim Dempsey,

 

Thank you so much I could rectify this error now. 

Santosh R

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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

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Beginner
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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

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Honored Contributor I
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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:

 

 

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