Re: Strange occurence of NaN

[Matthew Mitchell]

Thanks for your reply Marcus,

Like you, the first thing I did was write a small program to test it and
see what happened.  However, I did this again executing your program with
a loop (and a few changes to the compile command.  I am actually using
egcs). The NaN problem didn't occur.

Here is the compile command I used and its result (in case there is
something I left out):

 /usr/local/bin/libtool-swarm --mode link egcs -O2 -o main -Wall -Werror
-Wno-import -g -L/usr/local/lib -I/usr/local/include/swarm -L/usr/lib/
-rpath /usr/local/lib -rpath /usr/lib -I/usr/local/include
-L/usr/X11R6/lib main.m -lspace -lspace -lanalysis -lsimtools
-lsimtoolsgui -ltkobjc -ltclobjc -lactivity -lrandom -lobjectbase
-lcollections -ldefobj -lmisc -lBLT -ltk8.0 -ltcl8.0 -lpng -lz -lffi -lm
-lobjc -lpthread -ldl -lposix -lXpm -lX11
egcs -O2 -o main -Wall -Werror -Wno-import -g -L/usr/local/lib
-I/usr/local/include/swarm -L/usr/lib/ -I/usr/local/include
-L/usr/X11R6/lib main.m -lspace -lspace -lanalysis -lsimtools
-lsimtoolsgui -ltkobjc -ltclobjc -lactivity -lrandom -lobjectbase
-lcollections -ldefobj -lmisc -lBLT -ltk8.0 -ltcl8.0 -lpng -lz -lffi -lm
-lobjc -lpthread -ldl -lposix -lXpm -lX11 -Wl,--rpath -Wl,/usr/local/lib
-Wl,--rpath -Wl,/usr/lib

Here is the code I ran:

#import <simtools.h> // Need this for some reason
#import <defobj/Create.h>

@interface AgentModel: CreateDrop
- (double)getLearningRate;
@end
  
@implementation AgentModel     
- (double)getLearningRate
{
  return 0.2;
}
@end
 
int
main (int argc, const char **argv)
 {
   double tempStrength = 0.0;   
   double rewardStrength = 0.0;
   double Qreturn = 0.0;
   double discountRate = 0.9;
   id agentModel;
   int x = 0;

   initSwarmApp (argc, argv, "1.4.1", "address@hidden");
   //   initSwarmBatch (argc, argv);
    
   agentModel = [AgentModel create: globalZone];
 
   for (x=0;x<1000;x++) {
     tempStrength = tempStrength +
       ([agentModel getLearningRate] *
        ((rewardStrength + (discountRate * Qreturn)) - tempStrength));
     printf ("%f\n", tempStrength);
   }
   return 0;
 }


In the actual code all variables (including the return type) are doubles.

The problem does NOT seem to occur when I remove the two occurences of
"-O2" option from Makefile.common. Nor does it occur if I use "-O1".

I did not realise optimization was turned on, so thanks for
pointing that out.  Yesterday I found a work-around to the problem by
splitting the statement into 2 as follows:

    tempValue = ((rewardStrength + (discountRate * Qreturn)) 
           - tempStrength)
    tempStrength = tempStrength + [agentModel getLearningRate] 
            * tempValue;

But that is a bit dodgy, and doesn't instill much confidence that
the problem won't re-occur somewhere else later. 

Thanks for your help Marcus, I think I will stick to using optimization
option -O1 and see how that goes.

Matt


On Wed, 17 May 2000, Marcus G. Daniels wrote:

> >>>>> "MM" == Matthew Mitchell <address@hidden> writes:
> 
> MM> I have noticed I am getting NaN's occuring. 
> 
> Is this all `double' arithmetic, including the return type of
> getLearningRate?
> 
> Does it go away when optimization is off?
> 
> Can you make this program exhibit the behavior?
> 
> #import <simtools.h>
> #import <defobj/Create.h>
> 
> @interface AgentModel: CreateDrop
> - (double)getLearningRate;
> @end
> 
> @implementation AgentModel
> - (double)getLearningRate
> {
>   return 0.2;
> }
> @end
> 
> int
> main (int argc, const char **argv)
> {
>   double tempStrength = 0.0;
>   double rewardStrength = 0.0;
>   double Qreturn = 0.0;
>   double discountRate = 0.9;
>   id agentModel;
> 
>   initSwarmBatch (argc, argv);
> 
>   agentModel = [AgentModel create: globalZone];
> 
>   tempStrength = tempStrength +
>     ([agentModel getLearningRate] *
>      ((rewardStrength + (discountRate * Qreturn)) - tempStrength));
>   
>   printf ("%f\n", tempStrength);
>   return 0;
> }
> /*
> Local Variables:
> compile-command: "$SWARMHOME/bin/libtool-swarm --mode=link gcc -O2 -o diff 
> -Wall -Werror -g -Wno-import -I$SWARMHOME/include/swarm 
-L$SWARMHOME/lib/swarm diff.m -lswarm -lobjc"
> End:
> */
> 
>                   ==================================
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