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pFq: Add rescaling if term when b crosses the origin underflows.

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jzmaddock
2019-04-05 18:54:10 +01:00
parent 805161a5c8
commit 9b0d249f68
1 changed files with 19 additions and 3 deletions
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22
include/boost/math/special_functions/detail/hypergeometric_pFq_checked_series.hpp
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@@ -114,9 +114,11 @@
{
if (k < crossover_locations[n])
{
for(auto ai = aj.begin(); ai != aj.end(); ++ai)
for (auto ai = aj.begin(); ai != aj.end(); ++ai)
{
if ((*ai < 0) && (floor(*ai) == *ai) && (*ai > crossover_locations[n]))
return std::make_pair(result, abs_result); // b's will never cross the origin!
}
//
// b hasn't crossed the origin yet and the series may spring back into life at that point
// so we need to jump forward to that term and then evaluate forwards and backwards from there:
@@ -147,8 +149,22 @@
if (z < 0)
s1 *= (s & 1 ? -1 : 1);
term -= local_scaling;
//std::cout << "term = " << term << std::endl;
if (term > -tools::log_max_value<Real>())
if (term <= tools::log_min_value<Real>())
{
// rescale if we can:
int scale = itrunc(floor(term - tools::log_min_value<Real>()));
if (scale < tools::log_max_value<Real>())
{
Real ex = exp(Real(-scale));
if (tools::max_value<Real>() / ex > result)
{
term -= scale;
log_scale += scale;
result *= ex;
}
}
}
if (term > tools::log_min_value<Real>())
{
if (term > 10)
{