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<p>
This package provides classes to handle sampling steps during
Ordinary Differential Equations integration.
</p>

<p>
In addition to computing the evolution of the state vector at some grid points, all
ODE integrators also build up interpolation models of this evolution <em>inside</em> the
last computed step. If users are interested in these interpolators, they can register a
{@link org.apache.commons.math.ode.sampling.StepHandler StepHandler} instance using the
{@link org.apache.commons.math.ode.FirstOrderIntegrator#addStepHandler addStepHandler}
method which is supported by all integrators. The integrator will call this instance
at the end of each accepted step and provide it the interpolator. The user can do
whatever he wants with this interpolator, which computes both the state and its
time-derivative. A typical use of step handler is to provide some output to monitor
the integration process.
</p>

<p>
In a sense, this is a kind of Inversion Of Control: rather than having the master
application driving the slave integrator by providing the target end value for
the free variable, we get a master integrator scheduling the free variable
evolution and calling the slave application callbacks that were registered at
configuration time.
</p>

<p>
Since some integrators may use variable step size, the generic {@link
org.apache.commons.math.ode.sampling.StepHandler StepHandler} interface can be called
either at regular or irregular rate. This interface allows to navigate to any location
within the last computed step, thanks to the provided {@link
org.apache.commons.math.ode.sampling.StepInterpolator StepInterpolator} object.
If regular output is desired (for example in order to write an ephemeris file), then
the simpler {@link org.apache.commons.math.ode.sampling.FixedStepHandler FixedStepHandler}
interface can be used. Objects implementing this interface should be wrapped within a
{@link org.apache.commons.math.ode.sampling.StepNormalizer StepNormalizer} instance
in order to be registered to the integrator.
</p>

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