matter@milton.u.washington.edu (Matthew Trunnell) (07/06/90)
We have been having a continuing series of problems with the Fortran
compliler on the DS3100. We are running UWS2.1 and I have just installed
v2.1 of the f77 which was supposed to fix some bugs in the earlier unsupported
release of v2.1 and v2.0.
The problem appears unpredictably with either -O2 or -O3 optimization
specified. The symptom is that the executible runs fine but gives the wrong
numbers with the higher optimization. Even I could write a compiler to
produce fast code if the answers didn't matter...
Here is a sample of the problem. The source code (included below) was written
by a student with no claims of being a programmer, so I have not entirely
ruled out the possibility that some of the difficulty arises from non-standard
language use.
-----------------------------------------------------------------------------
snapper% f77 -o test parker.f
snapper% f77 -o test2 -O2 parker.f
snapper% test
tau 3.604890
ttime 113
7.1585506E-02 0.0000000E+00
6.3956492E-02 -0.0000000E+00
snapper% test2
tau 3.604890
ttime 113
7.1585506E-02 0.0000000E+00
5.2087046E-03 -0.0000000E+00
snapper%
-----------------------------------------------------------------------------
Incidentally, the unoptimized result above agrees with every other compiler I
have tried.
There seems to be some sensitivity to the position of comments and
never-executed lines in the source code.
Has anyone had similar problems? Is there some way of assuring that accurate
code will be generated?
Thanks for your time.
matter
-----------------------------------------------------------------------------
Matthew Trunnell Ec-2 matter@ocean.washington.edu
-----------------------------------------------------------------------------
Here is the source for parker.f:
program test
c ********* variables ***********
real u0(0:400),u1(0:400),v0(0:400),v1(0:400)
real b0(0:400),b1(0:400)
real f,n,alpha,vee,dt,dz,s,s1,z
real nu,kappa,ds,tau0
real ff,ral,nn,m0,t,tau,sal
real m,interval,d1b,d2b,d3b,nc
integer i,j,ns,nt,depth,ttime,looktime,looktau
c
c ************ data ************
data f,n,nu /1.0,2.0,.01/
data depth /10/
data dz,dt /.025,.005/
alpha=15.
kappa=0.
vee=-1.
looktau=5
c ********* setting some values ************
ral=2.0*3.14159*alpha/360.0
ff=f*cos(ral)
ds=(2.*nu/ff)**.5
nn=n*n*sin(ral)
nc=n*n*cos(ral)
tau0=ff/(nn*sin(ral))
s=ff*tau0
s1=(1.+s)/s
tau=tau0*(1.+2.*kappa/(vee*ds*tan(ral)))**-1
m0=-vee*ds/2.0
sal=sin(ral)
ns=int(depth/dz)
looktime=int(tau*looktau)
ttime=int(30.*tau)+5
print*,'tau',tau
print*,'ttime',ttime
nt=int(ttime/dt)
interval=1./dt
c ********** Ekman Initial Condition **********
100 do 110 i=0,ns
z=dz*float(i)
u0(i)=-vee*sin(z/ds)*exp(-z/ds)
v0(i)=vee*(1.-cos(z/ds)*exp(-z/ds))
b0(i)=0.
110 continue
c
c ******* timeloop *******
300 do 1000 i=0,300
t=float(i)*dt
c
c ****** solving the difference equations *******
400 do 500 j=1,ns-1
d1b=nu*(u0(j+1)-2.*u0(j)+u0(j-1))/dz**2
u1(j)=u0(j)+dt*(ff*(v0(j)-vee)-sal*b0(j)+d1b)
d2b=nu*(v0(j+1)-2.*v0(j)+v0(j-1))/dz**2
v1(j)=v0(j)+dt*(-ff*u0(j)+d2b)
d3b=kappa*(b0(j+1)-2.*b0(j)+b0(j-1))/dz**2
c---------------------------------------------------------------------c
c The following never-true IF statement prevents the uopt from
c choking.
c---------------------------------------------------------------------c
c if(d3b.ne.0.)stop("SPAM")
c b1(j)=b0(j)+dt*(nn*u0(j)+d3b)
b1(j)=b0(j)+dt*(nn*u0(j))
500 continue
c
c ******* boundary conditions *********
u1(0)=0.
v1(0)=0.
b1(0)=0.
u1(ns)=u1(ns-1)
v1(ns)=v1(ns-1)
b1(ns)=b1(ns-1)
c
c ****** branch to read transport values or not *********
if(mod(i,interval).eq.0)then
goto 520
else
goto 700
endif
c
c ****** read values to transport output file *********
520 m=0.
600 do 610 j=0,ns-1
m=m+dz*(u0(j)+u0(j+1))/2.0
610 continue
write(6,*)m,d3b
c ****** resetting the variables before the next timestep *****
700 do 800 j=0,ns
u0(j)=u1(j)
v0(j)=v1(j)
b0(j)=b1(j)
800 continue
c
c ******* closing the timeloop *******
1000 continue
end