Re: log2 calculations, entropy

[Marcus G. Daniels]

>>>>> "PJ" == Paul Johnson <address@hidden> writes:

PJ> I can't figure how to get a logarithm to the base 2. 

#import <misc.h> // M_LN2, log, atof, printf

double log2 (double val)
{
  return log (val) / M_LN2;
}

int
main (int argc, const char **argv)
{
  printf ("%f\n", log2 (atof (argv[1])));
}

/*
Local Variables:
compile-command: "/opt/gnu/bin/gcc -o log2 -g -Wno-import 
-L/opt/SUNWtcl/8.0/sun4/lib -R/opt/SUNWtcl/8.0/sun4/lib -L/opt/SDGblt/2.4g/lib 
-R/opt/SDGblt/2.4g/lib -L/opt/SDGlibffi/1.20/lib -R/opt/SDGlibffi/1.20/lib 
-L/opt/SDGswarm/1.4.1/lib -L/opt/SDGzlib/1.1.3/lib -L/usr/local/X11/lib 
-R/usr/local/X11/lib -L/usr/openwin/lib -R/usr/openwin/lib 
-L/opt/SDGhdf5/1.0.1/lib -I/opt/SDGswarm/1.4.1/include log2.m -lanalysis 
-lsimtools -lsimtoolsgui -lactivity -ltkobjc -lrandom -lobjectbase  -ldefobj 
-lcollections -lmisc  -ltclobjc -ltk8.0 -ltcl8.0 -lBLT -lsocket -ldl -lnsl 
-L/usr/openwin/lib -lhdf5 -lpng -lz -lXpm -lX11 -lffi -lm -lobjc -lpthread 
-lposix4"
End:
*/

PJ> While looking for an answer, I notice in the swarm
PJ> src/analysis/Entropy.m, that the natual log is used to calculate
PJ> entropy, not log base 2.  If Balch is correct, the current method is
PJ> wrong.

Notice the denominator in `log2' is a constant.

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