!!Simulation methods

SimTree tries to support the user in performing methodical correct studies. For this
it has built-in rules for the control of simulation studies and for consistency checks
of the state of the results tree and the results in the tree.

SimTree support two simulation methods:

%inc parts method-bm

%inc parts method-ir

Besides this, there are two modes of operation: 

* First, for each simulation parameter value set
  the simulation program may be started to generate the results for this
  parameter value set. These results are called FinalResults and they are
  directly usable to be queried or evaluated. This "one-step" simulation
  is only applicable for the BM method. The number of batches may be
  specified with the [@o]--batches option.
  
* Second, for each simulation parameter value set the
  simulation program may be started with different start values for the
  random number generator (so called seed).

. In this mode only preliminary results (export results) are generated which
  have to be collected in a separate run of the simulation program to generate
  FinalResults for this parameter value set.
  
. This "two-step" simulation is applicable both for the BM and for the IR
  method. For the BM method the number of batches may be specified with the
  [@o]--batches option. For the IR method the number of drops may be specified
  with the [@o]--drops option. 

In the first mode batches are called default batches (with a default seed). In
the second mode so called seeded results (drops or batches)
are obtained. For the BM method default batches and seeded results may be intermixed in one results
tree: For each simulation parameter value set a different combination of
batches and seeds may be selected.

A results tree is in one of three simulation modes:

* The simulation method is not yet set. This is the case when the tree
  contains no results (is empty).
  
* The simulation method is BM. Then only default batch results or seeded results
  requested with the [@o]--batches option may be generated.
  
* The simulation method is IR: Then only seeded drop results may be requested
  with the [@o]--drops option.

The exact behavior of SimTree for these two supported methods is defined in the
next chapter.
