compiler problem - comp.lang.fortran

Message from discussion compiler problem

Steven G. Kargl

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More options May 8, 1:38 pm

Newsgroups: comp.lang.fortran

From: ka...@troutmask.apl.washington.edu (Steven G. Kargl)

Date: Thu, 8 May 2008 17:38:04 +0000 (UTC)

Local: Thurs, May 8 2008 1:38 pm

Subject: Re: compiler problem

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In article <c28af821-e279-42f8-8b8c-16204ef43...@p25g2000pri.googlegroups.com>,
rudra <bnrj.ru...@gmail.com> writes:

> hello friends,
> i was just trying to see the performance of different compiler
> (gfortran and ifort) and there is a problem inthis part of the code:
> "===============Creating Initial Configuration=============="
> 58 write(*,&
> 59 '(1x,"Minimum distance between any two particle is",
> 1x,f6.4)'),rcut !rcut=1.5
> 60 !-----------------------------------------------
> 61 ! INITIALISE POSITION
> 62 !-----------------------------------------------
> 63 10 do i=1,ntot
> 64 x(i)=boxl*(ran(seed)-0.0)
> 65 y(i)=boxl*(ran(seed)-0.0)
> 66 z(i)=boxl*(ran(seed)-0.0)

Why subtract 0.0?

> 67 call pbc(x,y,z,boxl)
> 68 end do
> 69 !- - - - - - - - - - - - - - - - - - - - - - - -
> 70 ! KEEPING MINIMUM DIST. BETWEEN ANY TWO
> 71 ! ATOM GREATER THEN RCUT
> 72 !- - - - - - - - - - - - - - - - - - - - - - - -

rcut2 = rcut**2

> 73 do i=1,nap-1
> 74 do j=i+1,nap
> 75 dx=x(i)-x(j)
> 76 dy=y(i)-y(j)
> 77 dz=z(i)-z(j)
> 78
> 79 dist=dsqrt(dx*dx+dy*dy+dz*dz)

Depending on the value of nap, it may be prudent to do

dist2 = dx*dx+dy*dy+dz*d

> 80 tr=tr+1
> 81 ! write(*,*) tr
> 82 if (dist<rcut)go to 10

if (dist2 < rcut2) goto 10

> 83 end do
> 84 end do
> 85 write(*,'(1x,"Success after",1x,i0,1x,"try")')tr
> 86 call mindist(x,y,z)
> 87 write(*,*) &
> 88
> "==========================================================="
> 89 write(*,*) ""
> 90
> 91 !-----------------------------------------------
> 92 ! INITIAL CONFIGURATION DONE
> 93 !-----------------------------------------------
> while compiling with ifort, its converging after 160k steps, but even
> after waiting for 1000k steps with gfortran, its not
> converging......do you think its problem with ran? can you suggest a
> better way?

What is seed? What is boxl()?

program a
integer i, seed
seed = 0
do i = 1, 4
print *, ran(seed)
end do
print *
seed = 1
do i = 1, 4
print *, ran(seed)
end do
seed = 42
do i = 1, 4
print *, ran(seed)
end do
end program a

RTFM?

--
Steve
http://troutmask.apl.washington.edu/~kargl/

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