This module is devoted to migrating from Apache Commons Math to Hipparchus.

The module provides a transition script and a temporary migration jar. The migration process is composed of several phases:

  • make sure you don't use any class that has been already deprecated in Apache Commons Math
  • run the migration script on the application source
  • modify the build configuration to use Hipparchus modules instead of Apache Commons Math jar
  • fix the (hopefully few) compilation errors that were not handled by the script
  • check everything runs, ignoring the warnings about deprecated interfaces that are provided by the intermediate hipparchus-migration jar
  • progressively get rid of the deprecated interfaces, following the deprecation statements hints
  • remove the dependency to the intermediate hipparchus-migration jar

Modifying the build configuration

As your application depended on Apache Commons Math which as only one jar, your build system knows about this jar. It has to be replaced by the various jars provided by Hipparchus. All uses will at least need the hipparchus-core jar. Complex uses may need all the jars.

The simplest way to identify which jars you need is to add them one by one, looking at the compilation errors. This is easy and fast as there are only a dozen jars and you will certainly not depend on some of them (hipparchus-perf and hipparchus-samples are typically not used). The first jar that will be mandatory is hipparchus-core. If this one is not sufficient, the second one to add is hipparchus-migration because it adds some glue code for migration that is often needed. Then add other jars depending on the compilation errors you get, looking only at the package names of the missing classes.

Fixing compilation errors

There may be some problems not handled by the script. The known problems are the following ones:

  • specific exceptions not thrown anymore. The huge number of specialized exception has been drastically reduced with only MathIllegalArgumentException, MathIllegalStateException, both of which extending MathRuntimeException. The specialize NullArgumentException which extends the Java language standard NullPointerException and should almost never been caught. The recommended way to catch Hipparchus exceptions is therefore to catch only MathRuntimeException and to call the new getSpecifier method if you are really looking for a specific exception, which is a very rare need.
  • getContext() method, ExceptionContextProvider interface and ExceptionContext class not found. The exception context feature that was present in Apache Commons Math has been merged into the MathRuntimeException base class. Its getValue(key) method is essentially replaced by getParts[index].
  • classes from packages org.apache.commons.math[34].geometry.partitioning.utilities or org.apache.commons.math[34].optimization not found almost all the classes that were already deprecated in Apache Commons Math have been removed from Hipparchus, users must replace them before performing the migration.
  • method derivative() in class PolynomialFunction not found. Despite this method was not deprecated it was removed as superseded by the already existing polynomialDerivative method which is fully compatible with it as it returns a more specialized type
  • getDimension() and getFirstIndex() not found inEquationsMapperandgetSecondaryMappers()not present inExpandableODE. There is now only one equations mapper for both the primary equation and the various secondary equations in an ODE, so the way to map the composite state into primary and secondary states is different, and in fact much simpler. Users must retrieve the single mapper by callinggetMapper()` and then get directly the primary and secondary states from this single mapper.
  • Action enumerate not found. The Action enumerate used as a return value in events handlers eventOccurred method was an internal enumerate defined in the EventHandler interface, so no dedicated import statement was needed. It is now a separate enumerate, shared by both the double-based and field-based events handlers, and needs to be imported specifically.
  • conflicts between application class names and Apache Commons Math class names. As the script is based on text substitution without knowledge about the Java language syntax, names from the application may be confused by the script with similar names in the Apache Commons Math library even if they are in different packages. Such names may be converted despite they should not be touched, so the change must be reverted manually for these classes.

Checking everything runs

Once everything compiles, you should run your application tests to see if everything runs. If not, ask to the developers mailing lists.

Deprecation warnings at this step are normal. They correspond to APIs that were present in Apache Commons Math and have been modified in Hipparchus. In order to help users switch, we have moved these APIs in the hipparchus-migration jar and they act as facades between user code and the new Hipparchus APIs. They are marked as deprecated so users can easily spot them and change to the newer APIs progressively while still having a running application.

Getting rid of the deprecated interfaces

When the application runs in a full Hipparchus environment, you can start updating your code to use the new APIs provided by Hipparchus. This is just a traditional maintenance task. The deprecation hints in the hipparchus-migration sources will help you find the new interfaces. They are often very close to the previous ones and modification is expected to be straightforward.

If you want to get rid of all problems at once, you can also remove the migration jar from your build configuration, so instead of deprecation warnings, you will get compilation errors which are easier to spot in integrated development environments.

Removing the dependency to the intermediate hipparchus-migration jar

When all deprecation warnings have been fixed, you can safely remove the hipparchus-migration jar from your build system, everything should work.

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Version: 3.1. Last Published: 2024-04-02.

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