position dependent photon field for EM interactions (optimised) by GDMarco · Pull Request #535 · CRPropa/CRPropa3

GDMarco · 2026-01-26T17:53:54Z

General description

This is a fully working version of the CRPropa code with some implementation to allow spatially dependent photon field to be initialised and employed for electromagnetic interactions. A particular example is the introduction of the galactic interstellar field (the density and interaction rate tables are at this repo: ISRF tables.)
In principle, this implementation can be used for any spatial dependent photon field properly build by the user.
To allow the introduction of such spatially variable photon fields in CRPropa, the classe and modules that have been modified arePhotonBackground.*, EMPairProduction.*, EMDoublePairProduction.*, EMInverseComptonScattering.* and EMTripletPairProduction.*. Moreover, the class InteractionRates.* has been implemented to handle the process rates.
An example on how to use the code is contained in the notebooks.

Technical details

The .cc files of PhotonBackground.*,EMPairProduction.*, EMDoublePairProduction.*, EMInverseComptonScattering.* and EMTripletPairProduction.* employ some tools of the #include <filesystem> library, only available since C++17. The proper library is specified in the CMakeLists.txt files, as well as in the header of the .cc files.

The code uses the nanoflann functionalities to look for the closest photon field point in your custom grid and evaluate the density and/or the rate correctly. In this new version, nanoflann is implemented as a header-only library among the ones in the /libs/ directory.

//InteractionRatesIsotropic::InteractionRatesIsotropic(); //InteractionRatesIsotropic::InteractionRatesPositionDependent();

Changing nomenclature (isSpatialDependent -> isPositionDependent).

Changing nomenclature

Change nomenclature.

…n field

…ckground

style & constructor of InteractionRates subclasses

JanNiklasB

Hi,

thanks for your contribution!
I have done a first review of your pull request and noticed the following things.

Please try to not include lines in your pull request that are only altered in white spaces without having any purpose, you often only change tabs to spaces or add new empty lines, this makes it difficult to spot actual changes and leads to difficult to read code.
Reduce the amount of includes you use in your files, any not needed include or already in the header existing includes should not be in the .cpp file again. This is only a style thing since otherwise the code seems a little cluttered.
For the 4 changed module files (EM*.h and EM*.cpp) I only commented in EMDoublePairProduction.* but my comments hold true for all module files:
-> The old behavior of function and classes regarding function calls can not be changed, it needs to be backwards compatible ( We need to at least notify the community first when we remove or change crucial features)
-> Everything needs to be as modular as possible, so if you use a class like the interaction rates in a function you need to only require the base class so the user can create their own versions and hand them over. Those base classes then need everything to distinguish them inside those functions
You require the function splitFilename in many of your classes but this function does not depend on any class member, so it would be better to add this function to Common.h as a standalone
Every function which is not obvious to use or where it is not obvious what it does needs to have a description
You need to add your changes to the change log CHANGELOG.md

Many comments would repeat themself so I usually mention something only 1 or 2 times.

With regards,
Jan-Niklas

JanNiklasB · 2026-02-13T13:02:43Z

src/module/EMDoublePairProduction.cpp

 #include "crpropa/Random.h"
+#include "crpropa/PhotonBackground.h"
+#include "crpropa/InteractionRates.h"
+#include "crpropa/Geometry.h"


PhotonBackground.h, InteractionRates.h and Geometry.h are already included in the corresponding EMDoublePairProduction.h header. Please remove them here for style reasons.

JanNiklasB · 2026-02-13T13:06:54Z

include/crpropa/module/EMDoublePairProduction.h

+   @param thinning		weighted sampling of secondaries (0: all particles are tracked; 1: maximum thinning)
+   @param limit			step size limit as fraction of mean free path
+   @param surface     suface to enclose the grid nodes to be loaded
+   @param interactionRates(hidden)  object to store and access to the interaction rates of the process


The interactionRates should not appear as parameter since the user is not able to actually specify them that way. Instead mention them in the description of the constructor like for example:

/** Constructor * You can set interactionRates via initRate(std:.string filename) * .... * /

JanNiklasB · 2026-02-13T13:08:43Z

include/crpropa/module/EMDoublePairProduction.h

+   * @param surface closed surface to confine the grid to be  uploaded
+   */
+  void setSurface(ref_ptr<Surface> surface);
+  bool hasSurface() const;


It might be better to return the Surface pointer instead, that way the user can do the check and still use the pointer afterwards.

JanNiklasB · 2026-02-13T13:11:42Z

include/crpropa/module/EMDoublePairProduction.h

+  std::string getInteractionTag() const;
+
+  void initRate(std::string filename, InteractionRatesHomogeneous* intRatesHom);
+  void initRatePositionDependentPhotonField(std::string filepath, InteractionRatesPositionDependent* intRatesPosDep);


A description of initRate and initRatePositionDependentPhotonField is necessary, it is not clear for the average user how to use those functions.

Furthermore, we might need to add a initRate(std::string) overload so the old call behavior is preserverd.

JanNiklasB · 2026-02-13T13:50:39Z

src/module/EMDoublePairProduction.cpp

+  if (!this->photonField->hasPositionDependence()) {
+
+    this->interactionRates = new InteractionRatesHomogeneous("interactionRatesHomogeneous", false);
+    InteractionRatesHomogeneous* intRatesHom = static_cast<InteractionRatesHomogeneous*>(this->interactionRates.get());


With the requested change of initRate in the header file this pointer and the one in line 51 are not required. Furthermore initRate would be used in both cases so the if condition would is then only required inside the initRate function.

JanNiklasB · 2026-02-13T16:42:28Z

src/PhotonBackground.cpp

-		initRedshiftScaling();
+  this->isPositionDependent = isPositionDependent;
+
+  if (this->isPositionDependent) {


instead of throwing an error when the user sets isPositionDependent=true remove the argument from the constructor and just set it manually to false

JanNiklasB · 2026-02-13T16:47:37Z

src/PhotonBackground.cpp

+    } else if (!this->isPositionDependent) { 
+
+        throw std::runtime_error("Photon Field " + fieldName + " is not position dependent! It is not the correct class. \n");
+


Like above, if you do not want to have a RedshiftDependence then don't give the user the option to set it

JanNiklasB · 2026-02-13T16:53:30Z

include/crpropa/PhotonBackground.h

+ */
+class TabularSpatialPhotonField: public PhotonField {
+public:
+    TabularSpatialPhotonField(const std::string fieldName, const bool isRedshiftDependent = true, const bool isPositionDependent = true, ref_ptr<Surface> surface = nullptr);


If the field is not dependent on Redshift or Position, then it would be better to manually set them to false instead of giving the user the option to set them here. Also, since the options are set to true by default and the constructor throws an error when that happens, the user probably is forced to set them to false in every case.

JanNiklasB · 2026-02-13T17:00:08Z

CMakeLists.txt

+if(APPLE)
+    message(STATUS "Building on macOS, using C++11")
+    set(CMAKE_CXX_STANDARD 11)
+#    set(CMAKE_CXX_STANDARD_REQUIRED ON)


Is there something on macOS that prevents us to set this CXX standard to required? If not it would be good to uncomment this I think.

JanNiklasB · 2026-02-13T17:03:29Z

CMakeLists.txt


 endif(ENABLE_PYTHON AND Python_FOUND)

+target_include_directories(crpropa


Please add nanoflann to crpropa over CRPROPA_EXTRA_INCLUDE and CRPROPA_EXTRA_SOURCES (see other libraries).

GDMarco added 30 commits March 5, 2024 16:40

creating InteractionRates class

bd15e91

InteractionRates class in SWIG

4efbaa5

update CMakeLists.txt

1c9085e

correct InteractionRates.cpp #include

0bb1fec

avoid redefinition in InteractionRates.cpp

cfa0371

outOfLine definition in InteractionRates.cpp

dc7b60c

//InteractionRatesIsotropic::InteractionRatesIsotropic(); //InteractionRatesIsotropic::InteractionRatesPositionDependent();

update PhotonBackground.h for space dependent fields

d4cc1c8

update PhotonBackground.cpp for space dependent fields

63f5573

update EMPairProduction.h/.cpp for space dependent fields

bf17391

correct #include for PhotonBackground.h/.cpp

68a1df2

correct #include in src/PhotonBackground.cpp

28dd755

correct src/EMPairProduction.cpp

60d904c

update files for position dependent background photons & EMPP

f88fd02

correct minor errors for position dependent photon field & EMPP

abf4d14

Update PhotonBackground.h

b26d064

Changing nomenclature (isSpatialDependent -> isPositionDependent).

Update PhotonBackground.cpp

bb502eb

Changing nomenclature

Update EMPairProduction.cpp

9067fa8

Change nomenclature.

Update EMPairProduction.h

7cad8ff

Change nomenclature.

update EMInverseComptonScattering.h/.cpp for position dependent photo…

e688abf

…n field

update EMDoublePairProduction.h/.cpp for position dependent photon ba…

d0b21b0

…ckground

update EMTripletPairProduction.h/.cpp for spatial dependent photon field

9e6b95c

Update InteractionRates.h

a5d9696

Update InteractionRates.h

9fbd61a

Update InteractionRates.cpp

f573b6f

style & constructor of InteractionRates subclasses

Update PhotonBackground.h indentation

149a771

style typos & methods in InteractionRates class

715ec1f

fix PhotonBackground.h for merging

01dc99e

change exit with throw std::runtime_error() & style

f501c69

Update CMakeLists.txt C++17

615f18c

Update (back) CMakeLists.txt to C++11 version

aeba158

GDMarco added 28 commits January 28, 2026 12:40

correcting _OSX.yaml

2669e52

correcting _OSX.yaml v1

8098c9a

correcting _OSX.yaml v2

e9c84dc

correcting _OSX.yaml v3

0dc79ee

correcting differences OSX and Ubuntu in calling filesystem

6188885

correcting ubuntu .yaml to C++17

8f59c6e

correcting ubuntu .yaml to C++17 v1

0e687fa

add stdfs++ to CMakeLists.txt

bb581d2

add stdfs++ to CMakeLists.txt v1

09d42f8

add stdfs++ to CMakeLists.txt v2

da8b4b5

add C++17 to ub22.yaml

424b0dc

change GCC version in CMake

63ad5c4

change GCC version in CMake v2 + in PhBkg

d26b64a

change GCC version in CMake v3

380cd68

try to fix PythonExtension test

3610079

try to fix PythonExtension and Interaction tests

9971827

add warnings for not finding posdepradfields

b9b5de3

add warnings for not finding posdepradfields v2

7d2a0dd

add --output for test

4f97506

donot test without tables

e185892

donot test without tables in testInt

4bb0728

donot test without tables in testInt v2

910461f

donot test without tables in testInt v3

00b3f41

donot test without tables in testInt v4

d5d04f0

donot test without tables in testInt v5 + EMPP

52ddb8e

donot test without tables in testInt v6

62e7085

donot test without tables in testInt v7 + EMPP v2

49d1d63

EMPP v3

8285960

GDMarco marked this pull request as ready for review February 12, 2026 14:24

JanNiklasB suggested changes Feb 13, 2026

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position dependent photon field for EM interactions (optimised)#535

position dependent photon field for EM interactions (optimised)#535
GDMarco wants to merge 120 commits intoCRPropa:masterfrom
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		} else if (!this->isPositionDependent) {

		throw std::runtime_error("Photon Field " + fieldName + " is not position dependent! It is not the correct class. \n");


		endif(ENABLE_PYTHON AND Python_FOUND)

		target_include_directories(crpropa

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GDMarco commented Jan 26, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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GDMarco commented Jan 26, 2026 •

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