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improvements in the way factorials are computed

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This commit is contained in:
Tiago Gomes 2012-04-18 02:46:38 +01:00
parent cd8714460e
commit d8e757f9ab
3 changed files with 15 additions and 20 deletions
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13
packages/CLPBN/clpbn/bp/Histogram.cpp
View File

@ -44,7 +44,7 @@ HistogramSet::operator[] (unsigned idx) const
unsigned
HistogramSet::nrHistograms (void) const
{
return Util::multichoose (size_, hist_.size());
return HistogramSet::nrHistograms (size_, hist_.size());
}
@ -77,7 +77,7 @@ HistogramSet::getHistograms (unsigned N, unsigned R)
unsigned
HistogramSet::nrHistograms (unsigned N, unsigned R)
{
return Util::multichoose (N, R);
return Util::nrCombinations (N + R - 1, R - 1);
}
@ -99,16 +99,17 @@ vector<double>
HistogramSet::getNumAssigns (unsigned N, unsigned R)
{
HistogramSet hs (N, R);
unsigned N_factorial = Util::factorial (N);
double N_fac = Util::logFactorial (N);
unsigned H = hs.nrHistograms();
vector<double> numAssigns;
numAssigns.reserve (H);
for (unsigned h = 0; h < H; h++) {
unsigned prod = 1;
double prod = 0.0;
for (unsigned r = 0; r < R; r++) {
prod *= Util::factorial (hs[r]);
prod += Util::logFactorial (hs[r]);
}
numAssigns.push_back (LogAware::tl (N_factorial / prod));
double res = N_fac - prod;
numAssigns.push_back (Globals::logDomain ? res : std::exp (res));
hs.nextHistogram();
}
return numAssigns;

18
packages/CLPBN/clpbn/bp/Util.cpp
View File

@ -84,8 +84,12 @@ double
logFactorial (unsigned num)
{
double result = 0.0;
for (unsigned i = 1; i <= num; i++) {
result += std::log (i);
if (num < 150) {
result = std::log (factorial (num));
} else {
for (unsigned i = 1; i <= num; i++) {
result += std::log (i);
}
}
return result;
}
@ -93,7 +97,7 @@ logFactorial (unsigned num)
unsigned
choose (unsigned n, unsigned k)
nrCombinations (unsigned n, unsigned k)
{
assert (n >= k);
int diff = n - k;
@ -117,14 +121,6 @@ choose (unsigned n, unsigned k)
unsigned
multichoose (unsigned n, unsigned k)
{
return choose (n + k - 1, k);
}
unsigned
expectedSize (const Ranges& ranges)
{

4
packages/CLPBN/clpbn/bp/Util.h
View File

@ -56,9 +56,7 @@ double factorial (unsigned);
double logFactorial (unsigned);
unsigned choose (unsigned, unsigned);
unsigned multichoose (unsigned, unsigned);
unsigned nrCombinations (unsigned, unsigned);
unsigned expectedSize (const Ranges&);