Test-incGamma: Added test application

This checks the consistency of incGamma and invIncGamma. It writes files
with columns containing values for different 'a' parameters. The
incGammaRatio_P.xy and invIncGammaRatio_P.xy files should generate the same
lines when the plot axis order is reversed. E.g., in gnuplot:

    plot "incGammaRatio_P.xy" us 1:5 w l, \
         "invIncGammaRatio_P.xy" us 5:1 w p

applications/test/incGamma/Make/files

@@ -0,0 +1,3 @@
+Test-incGamma.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-incGamma

applications/test/incGamma/Make/options

@@ -0,0 +1,5 @@
+EXE_INC = \
+    -I$(LIB_SRC)/sampling/lnInclude
+
+EXE_LIBS = \
+    -lsampling

applications/test/incGamma/Test-incGamma.C

@@ -0,0 +1,146 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     | Website:  https://openfoam.org
+    \\  /    A nd           | Copyright (C) 2023 OpenFOAM Foundation
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Application
+    Test-incGamma
+
+Description
+    This checks the consistency of incGamma and invIncGamma. It writes files
+    with columns containing values for different 'a' parameters. The
+    incGammaRatio_P.xy and invIncGammaRatio_P.xy files should generate the same
+    lines when the plot axis order is reversed. E.g., in gnuplot:
+
+        plot "incGammaRatio_P.xy" us 1:5 w l, \
+             "invIncGammaRatio_P.xy" us 5:1 w p
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+#include "mathematicalConstants.H"
+#include "rawSetWriter.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+using namespace Foam;
+using namespace Foam::constant::mathematical;
+
+scalar grade(const scalar f)
+{
+    return (Foam::cos(pi*(1 - f)) + 1)/2;
+}
+
+int main(int argc, char *argv[])
+{
+    const scalarField as({0.25, 0.5, 1, 2, 4});
+
+    static const scalar nXs = 10000;
+    static const scalar xMax = 10;
+    static const scalar nPs = 100;
+
+    wordList aNames(as.size());
+    forAll(as, ai)
+    {
+        aNames[ai] = name(as[ai]);
+    }
+
+    scalarField xs(nXs);
+    forAll(xs, xi)
+    {
+        const scalar f = grade(grade(scalar(xi)/(nXs - 1)));
+        xs[xi] = (1 - f)*small + f*xMax;
+    }
+
+    scalarField Ps(nPs);
+    forAll(Ps, Pi)
+    {
+        const scalar f = grade(grade(scalar(Pi)/(nPs - 1)));
+        Ps[Pi] = (1 - f)*rootVSmall + f*(1 - 1e-4);
+    }
+
+    #define DeclareTypePXs(Type, nullArg) \
+        PtrList<Field<Type>> Type##Ps(as.size()); \
+        PtrList<Field<Type>> Type##PErrors(as.size()); \
+        PtrList<Field<Type>> Type##Xs(as.size());
+    FOR_ALL_FIELD_TYPES(DeclareTypePXs);
+    #undef DeclareTypePXs
+
+    forAll(as, ai)
+    {
+        scalarPs.set(ai, new scalarField(nXs));
+        scalarPErrors.set(ai, new scalarField(nXs));
+        forAll(xs, xi)
+        {
+            const scalar P = incGammaRatio_P(as[ai], xs[xi]);
+            const scalar PStar =
+                incGammaRatio_P(as[ai], invIncGammaRatio_P(as[ai], P));
+            scalarPs[ai][xi] = P;
+            scalarPErrors[ai][xi] = mag(P - PStar);
+        }
+    }
+    forAll(as, ai)
+    {
+        scalarXs.set(ai, new scalarField(nPs));
+        forAll(Ps, Pi)
+        {
+            scalarXs[ai][Pi] = invIncGammaRatio_P(as[ai], Ps[Pi]);
+        }
+    }
+
+    rawSetWriter(IOstream::ASCII, IOstream::UNCOMPRESSED).write
+    (
+        ".",
+        "incGammaRatio_P",
+        coordSet(true, "x", xs),
+        aNames
+        #define TypePsParameter(Type, nullArg) , Type##Ps
+        FOR_ALL_FIELD_TYPES(TypePsParameter)
+        #undef TypePsParameter
+    );
+    rawSetWriter(IOstream::ASCII, IOstream::UNCOMPRESSED).write
+    (
+        ".",
+        "incGammaRatio_PError",
+        coordSet(true, "x", xs),
+        aNames
+        #define TypePErrorsParameter(Type, nullArg) , Type##PErrors
+        FOR_ALL_FIELD_TYPES(TypePErrorsParameter)
+        #undef TypePErrorsParameter
+    );
+    rawSetWriter(IOstream::ASCII, IOstream::UNCOMPRESSED).write
+    (
+        ".",
+        "invIncGammaRatio_P",
+        coordSet(true, "P", Ps),
+        aNames
+        #define TypeXsParameter(Type, nullArg) , Type##Xs
+        FOR_ALL_FIELD_TYPES(TypeXsParameter)
+        #undef TypeXsParameter
+    );
+
+    Info<< nl << "End" << nl << endl;
+
+    return 0;
+}
+
+
+// ************************************************************************* //