Re: [PATCH] Fix Bug 83237 - Values returned by std::poisson_distribution are not distributed correctly

[Michele Pezzutti <mpezz at tiscali dot it>]

I apologize as I am unable to run the test suitein its full form.

Nevertheless, I locally tested the following patch for the test suite:

*26_numerics/random/poisson_distribution/operators/values.cc
    Add additional test to cover bin 'floor(mu) + 1'

by compiling locally values.cc and running it as main().


I had to increase N from default value N = 100000 to N = 4000000 to 
trigger the fault.
I think that for smaller N, the deviation due to the bug is well within 
the confidence
interval set in testDiscreteDist().


The test case below is successful with the proposed patch.


diff --git a/values.cc b/values.cc
index 0039b7d..e12e54f 100644
--- a/values.cc
+++ b/values.cc
@@ -42,6 +42,10 @@ void test01()
   std::poisson_distribution<> pd3(30.0);
   auto bpd3 = std::bind(pd3, eng);
   testDiscreteDist(bpd3, [](int n) { return poisson_pdf(n, 30.0); } );
+
+  std::poisson_distribution<> pd4(37.17);
+  auto bpd4 = std::bind(pd4, eng);
+  testDiscreteDist<100, 4000000>(bpd4, [](int n) { return 
poisson_pdf(n, 37.17); } );
 }



On 12/11/2017 10:52 AM, Paolo Carlini wrote:
> Hi,
>
> On 10/12/2017 14:47, Michele Pezzutti wrote:
> > Hi.
> >
> > This patch intends to fix Bug 83237 - Values returned by 
> > std::poisson_distribution are not distributed correctly.
> > See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83237 for issue 
> > description and tests.
> In any case, the fix should come with a testcase, which would also 
> validate the analysis. For this discrete distribution should be pretty 
> easy to add one, because all the infrastructure is already in place, 
> essentially three lines added to 
> 26_numerics/random/poisson_distribution/operators/values.cc.
>
> Paolo.