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ENH: improve uniformity of Random::position<label>() (closes #865)

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- start/end values were underrepresented due to rounding.
  Now extend the range to include -0.5 and +0.5 beyond the usual
  range to ensure the same number density.
This commit is contained in:
Mark Olesen
2018-06-12 08:16:06 +02:00
parent dc521b95df
commit 3bcbb1615b
2 changed files with 30 additions and 14 deletions
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16
applications/test/Random/Test-Random.C
View File

@ -174,7 +174,21 @@ int main(int argc, char *argv[])
}
}
cout<< nl << "Done." << endl;
// Test uniformity of random
{
List<label> samples(20, Zero);
Random rnd(123456);
for (label i=0; i < 1000*samples.size(); ++i)
{
++samples[rnd.position<label>(0,19)];
}
Info<< nl << "uniform [0,20)" << nl << " "
<< flatOutput(samples) << nl;
}
Info<< nl << "Done." << endl;
return 0;
}

28
src/OpenFOAM/primitives/random/Random/Random.C
View File

@ -121,14 +121,16 @@ Foam::scalar Foam::Random::position
template<>
Foam::label Foam::Random::position(const label& start, const label& end)
{
return start + round(scalar01()*(end - start));
// Extend range from [0, N-1] to (-0.5, N-0.5) to ensure that round()
// results in the same number density at the ends.
return start + round(scalar01()*((end - start) + 0.998) - 0.499);
}
template<>
Foam::scalar Foam::Random::globalSample01()
{
scalar value = -GREAT;
scalar value(-GREAT);
if (Pstream::master())
{
@ -144,7 +146,7 @@ Foam::scalar Foam::Random::globalSample01()
template<>
Foam::label Foam::Random::globalSample01()
{
label value = labelMin;
label value(labelMin);
if (Pstream::master())
{
@ -160,7 +162,7 @@ Foam::label Foam::Random::globalSample01()
template<>
Foam::scalar Foam::Random::globalGaussNormal()
{
scalar value = -GREAT;
scalar value(-GREAT);
if (Pstream::master())
{
@ -176,16 +178,16 @@ Foam::scalar Foam::Random::globalGaussNormal()
template<>
Foam::label Foam::Random::globalGaussNormal()
{
scalar value = -GREAT;
label value(labelMin);
if (Pstream::master())
{
value = GaussNormal<scalar>();
value = GaussNormal<label>();
}
Pstream::scatter(value);
return round(value);
return value;
}
@ -196,16 +198,16 @@ Foam::scalar Foam::Random::globalPosition
const scalar& end
)
{
scalar value = -GREAT;
scalar value(-GREAT);
if (Pstream::master())
{
value = scalar01()*(end - start);
value = position<scalar>(start, end);
}
Pstream::scatter(value);
return start + value;
return value;
}
@ -216,16 +218,16 @@ Foam::label Foam::Random::globalPosition
const label& end
)
{
label value = labelMin;
label value(labelMin);
if (Pstream::master())
{
value = round(scalar01()*(end - start));
value = position<label>(start, end);
}
Pstream::scatter(value);
return start + value;
return value;
}