Custom input data

If you want to read custom user data, let's say to read a couple of check point for your time loop from file, here is some recipes of how to achieve that with simple helpers available in DuMu^x.

Read an array of numbers

If you have a simple text file containing a list of numbers

0.1
0.2
0.3
0.4

You can read these numbers into a std::vector<double> like this

#include <dumux/io/container.hh>
 
const auto numbers = Dumux::readFileToContainer<std::vector<double>>("numbers.txt");

The file extension is arbitrary. The container type std::vector<> needs to support begin(), end(), and push_back(). It has to have an alias value_type (the type of the element, here double) and this type needs to have an overloaded operator>> to be constructible from an input stream. With similar code you can also multi-column data like this

0.1 0.2 0.3
0.1 0.4 0.5

for example into a std::vector<Dune::FieldVector<float, 3>>

#include <dune/common/fvector.hh>
#include <dumux/io/container.hh>
 
const auto coords = Dumux::readFileToContainer<std::vector<Dune::FieldVector<double, 3>>>("coords.txt");

Read INI-style config data

You can read config data (key-value data) using the Dune::ParameterTreeParser. This is the same type of file we use for DuMu^x input files. Given a config file like this

[MyData]
InjectionRate = 0.1 0.2 0.3 0.4
BoundaryFlags = 3 4 5 6
 
[Problem]
EnableGravity = false

the data can be read into a Dune::ParameterTree like this

#include <dune/common/parametertreeparser.hh>
 
Dune::ParameterTree config;
Dune::ParameterTreeParser::readINITree("config.ini", config);

Again, the file extension is arbitrary. You can retrieve data by casting it into another type like this

const bool enableGravity = config.get<bool>("Problem.EnableGravity");
const auto boundaryFlags = config.get<std::vector<int>>("MyData.BoundaryFlags");

Read XML-formatted config data

XML (Extensible Markup Language) is a very flexible structured data format. You can read and write XML files using the TinyXML-2 library contained in DuMu^x. For example, given an XML file like this

<?xml version="1.0"?>
<!-- Simple custom data file -->
<InputData>
  <!-- Injection rates are in kg/s -->
  <InjectionRates>
  0.1 0.2 0.3 0.4
  </InjectionRates>
 
  <!-- BoundaryTypes: -1: no boundary, 0: Dirichlet, 1: Noflow, 2: Infiltration, 3: Outflow -->
  <BoundaryTypes>
  0 -1 -1 2
  </BoundaryTypes>
</InputData>

You can initialise the file reader like this

#include <dumux/io/xml/tinyxml2.h>
 
tinyxml2::XMLDocument xmlData;
const auto returnCode = xmlData.LoadFile("mydata.xml"); // extension arbitrary
if (returnCode != tinyxml2::XML_SUCCESS)
    DUNE_THROW(Dune::IOError, "Couldn't open XML file.");

and read fields like this

const tinyxml2::XMLElement* inputData = xmlData.FirstChildElement("InputData");
std::stringstream injectionData(inputData->FirstChildElement("InjectionRates")->GetText());
const auto injectionRates = readStreamToContainer<std::vector<double>>(injectionData);

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