ENH: histogram: output raw count, auto-range. Fixes #467

src/fileFormats/sampledSetWriters/gnuplot/gnuplotSetWriter.C

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2017 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -68,8 +68,18 @@ void Foam::gnuplotSetWriter<Type>::write
 ) const
 {
     os  << "set term postscript color" << nl
-        << "set output \"" << points.name() << ".ps\"" << nl
-        << "plot";
+        << "set output \"" << points.name() << ".ps\"" << nl;
+
+    // Set secondary Y axis if using two columns. Falls back to same
+    // values if both on same scale. However, ignore if more columns.
+    if (valueSetNames.size() == 2)
+    {
+        os  << "set ylabel \"" << valueSetNames[0] << "\"" << nl
+            << "set y2label \"" << valueSetNames[1] << "\"" << nl
+            << "set ytics nomirror" << nl << "set y2tics" << nl;
+    }
+
+    os  << "plot";
 
     forAll(valueSets, i)
     {
@@ -79,10 +89,14 @@ void Foam::gnuplotSetWriter<Type>::write
         }
 
         os  << " \"-\" title \"" << valueSetNames[i] << "\" with lines";
+
+        if (valueSetNames.size() == 2)
+        {
+            os  << " axes x1y" << (i+1) ;
+        }
     }
     os  << nl;
 
-
     forAll(valueSets, i)
     {
         this->writeTable(points, *valueSets[i], os);

src/functionObjects/field/histogram/histogram.H

@@ -58,6 +58,12 @@ Usage
         setFormat    | Output format           | yes         |
     \endtable
 
+Note
+    If max is not provided it will use the field's min and max as the bin
+    extremes. If max is provided but not min it will use 0. The set written
+    contains two columns, the first the volume averaged values, the second
+    the raw bin count.
+
 See also
     Foam::functionObject
     Foam::functionObjects::fvMeshFunctionObject