Add a first version of documentation about histograms #344
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tmadlener
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These histograms have a few caveats:
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jmcarcell
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Sep 26, 2025
| It might be necessary to monitor an algorithm, e.g. by keeping track of how many | ||
| times different branches in the algorithm logic are taken. Since Functional | ||
| algorithms run potentially multithreaded, the usual approach of simply using | ||
| mutable counters or histograms for this is not easily possible. Gaudi, provides |
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| mutable counters or histograms for this is not easily possible. Gaudi, provides | |
| mutable counters or histograms for this is not easily possible. Gaudi provides |
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| some threadsafe tools to make monitoring Functional algorithms possible more | ||
| easily. These tools generally take care of updating counters and histograms in a |
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| some threadsafe tools to make monitoring Functional algorithms possible more | |
| easily. These tools generally take care of updating counters and histograms in a | |
| some threadsafe tools to make monitoring Functional algorithms more easily | |
| possible. These tools generally take care of updating counters and histograms in a |
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| In Gaudi all of these tools live in the `Gaudi::Accumulators` namespace and we | ||
| refer to the [documentation of | ||
| that](ttps://gaudi.web.cern.ch/doxygen/v40r0/da/dd5/namespace_gaudi_1_1_accumulators.html) |
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| that](ttps://gaudi.web.cern.ch/doxygen/v40r0/da/dd5/namespace_gaudi_1_1_accumulators.html) | |
| that](https://gaudi.web.cern.ch/doxygen/v40r0/da/dd5/namespace_gaudi_1_1_accumulators.html) |
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| Histograms also exist as generic versions and as ROOT backed versions. The main | ||
| difference is that the ROOT backed version will obviously produce ROOTs | ||
| `TH[1-3][I,D,F]`s (and are hence also limited to at most 3 dimensions), where as |
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| `TH[1-3][I,D,F]`s (and are hence also limited to at most 3 dimensions), where as | |
| `TH[1-3][I,D,F]`s (and are hence also limited to at most 3 dimensions), whereas |
| // We can also just define the dimensions and the title | ||
| mutable Gaudi::Accumulators::RootHistogram<2> m_hist2d{this, "Hist2D", "A 2D histogram"}; | ||
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| // NOTE: For configurable histograms you ahve to register this empty callback |
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| // NOTE: For configurable histograms you ahve to register this empty callback | |
| // NOTE: For configurable histograms you have to register this empty callback |
| ```python | ||
| from Configurables import Gaudi__Histograming__Sink__Root as RootHistoSink | ||
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| histoSinkSvc = RootHistSink("RootHistoSink") |
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| histoSinkSvc = RootHistSink("RootHistoSink") | |
| histoSinkSvc = RootHistoSink("RootHistoSink") |
Change here or change above. In Gaudi it is only used once and with the o.
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| ### Customizing a histogram | ||
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| Configurable histograms need to be crated in `initialize` as follows in order to |
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| Configurable histograms need to be crated in `initialize` as follows in order to | |
| Configurable histograms need to be created in `initialize` as follows in order to |
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| ```cpp | ||
| auto operator()(/* However your signature looks like */) { | ||
| { // create a scope to limit the liftime of the buffer |
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| { // create a scope to limit the liftime of the buffer | |
| { // create a scope to limit the lifetime of the buffer |
| Configurable histograms need to be crated in `initialize` as follows in order to | ||
| pick up the configuration from python: | ||
| ```cpp | ||
| StatusCode MyAlgorithm::initizlize() { |
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| StatusCode MyAlgorithm::initizlize() { | |
| StatusCode MyAlgorithm::initialize() { |
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| Filling a histogram is done by using the `operator[]` of the histogram classes | ||
| and is the same, regardless of whether the histograms are configurable or | ||
| static, e.g. |
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| Filling a histogram is done by using the `operator[]` of the histogram classes | |
| and is the same, regardless of whether the histograms are configurable or | |
| static, e.g. | |
| Filling a histogram is done by using the `operator[]` of the histogram classes | |
| and is the same whether the histograms are configurable or | |
| static. |
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This is meant to be a basic introduction on how to use monitoring histograms. We should potentially also have a section about the underlying accumulators and maybe a few small examples.