ENH: FFT - updated for fft of real data

src/randomProcesses/fft/fft.C

@@ -34,6 +34,56 @@ namespace Foam
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+Foam::tmp<Foam::complexField> fft::realTransform1D(const scalarField& field)
+{
+    // Copy of input field for use by fftw
+    // - fftw requires non-const access to input and output...
+    scalarField fftInOut(field);
+
+    const label n = fftInOut.size();
+    const label nBy2 = n/2;
+
+    // Using real to half-complex fftw 'kind'
+    fftw_plan plan = fftw_plan_r2r_1d
+    (
+        n,
+        fftInOut.data(),
+        fftInOut.data(),
+        FFTW_R2HC,
+        FFTW_ESTIMATE
+    );
+
+    fftw_execute(plan);
+
+    fftw_destroy_plan(plan);
+
+    // field[0] = DC component
+    tmp<complexField> tresult(new complexField(nBy2 + 1));
+    complexField& result = tresult.ref();
+
+    result[0].Re() = fftInOut[0];
+    result[nBy2].Re() = fftInOut[nBy2];
+    for (label i = 1; i < nBy2; ++i)
+    {
+        result[i].Re() = fftInOut[i];
+        result[i].Im() = fftInOut[n - i];
+    }
+
+    return tresult;
+}
+
+
+Foam::tmp<Foam::complexField> fft::realTransform1D
+(
+    const tmp<scalarField>& tfield
+)
+{
+    tmp<complexField> tresult = realTransform1D(tfield());
+    tfield.clear();
+    return tresult;
+}
+
+
 void fft::transform
 (
     complexField& field,

src/randomProcesses/fft/fft.H

@@ -44,7 +44,6 @@ SourceFiles
 #define fft_H
 
 #include "complexFields.H"
-#include "UList.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -63,6 +62,19 @@ public:
     };
 
 
+    //- Transform real-value data
+    //  - uses the fftw real to half-complex method
+    //  - result size is field.size()/2 + 1
+    static tmp<complexField> realTransform1D(const scalarField& field);
+
+
+    //- Transform real-value data
+    //  - uses the fftw real to half-complex method
+    //  - result size is field.size()/2 + 1
+    static tmp<complexField> realTransform1D(const tmp<scalarField>& field);
+
+
+    //- Transform compex-value data
     static void transform
     (
         complexField& field,

src/randomProcesses/noise/noiseFFT/noiseFFT.C

@@ -26,7 +26,6 @@ License
 #include "noiseFFT.H"
 #include "IFstream.H"
 #include "DynamicList.H"
-#include "SubField.H"
 #include "mathematicalConstants.H"
 #include "HashSet.H"
 #include "fft.H"
@@ -240,33 +239,7 @@ Foam::tmp<Foam::scalarField> Foam::noiseFFT::Pf
     const tmp<scalarField>& tpn
 ) const
 {
-    // Calculate the 2-sided fft
-    // Note: result not scaled
-    tmp<scalarField> tPn2
-    (
-        mag
-        (
-            fft::reverseTransform
-            (
-                ReComplexField(tpn),
-                List<int>(1, tpn().size())
-            )
-        )
-    );
-
-    tpn.clear();
-
-    // Only storing the positive half
-    // Note: storing (N/2) values, DC component at position (0)
-    tmp<scalarField> tPn
-    (
-        new scalarField
-        (
-            scalarField::subField(tPn2(), tPn2().size()/2 + 1)
-        )
-    );
-
-    return tPn;
+    return mag(fft::realTransform1D(tpn));
 }
 
 

src/randomProcesses/windowModels/windowModel/windowModelTemplates.C

@@ -23,6 +23,10 @@ License
 
 \*---------------------------------------------------------------------------*/
 
+#include "SubField.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
 template<class Type>
 Foam::tmp<Foam::Field<Type>> Foam::windowModel::apply
 (