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3.12 Nonlinear Simplification Techniques 415
The level specification of CancelTerms does not correspond to the level of the internal
Mathematica representation of dae. Use ShowLevel (Section 3.12.6) or Statistics
(Section 3.6.17) to see which levels can be influenced by CancelTerms.
Ranking
Cancellation of terms is performed in a pre-calculated order which sorts the terms by increasing
influence. A method which estimates the influence of a cancellation on the output behavior is
called ranking. CancelTerms lets you choose which ranking method to use for each analysis mode
separately by means of the Ranking option. Possible values are:
{mode−>Automatic|Simulation, † † † }
set mode dependent ranking functions
Values for the Ranking option.
Automatic
Simulation
equivalent to {_−>Automatic}
equivalent to {_−>Simulation}
The ranking method can either be Automatic, which means to use the internal implemented ranking
function, or Simulation, which means to use the corresponding simulation function to calculate
the influence. The former is much more efficient while the latter is more accurate. If the option
value is the symbol Automatic or Simulation the corresponding ranking function is set for all
analysis modes simultaneously. If you want to set the ranking function for each mode separately,
you have to give a list of rules. The current analysis mode is then matched against the left hand
side of the rules and the corresponding right hand sides are chosen as ranking functions. Thus, mode
can either be one of the symbols DT or AC, or a pattern specification like _. The default setting is
Ranking −> Automatic.
RecordCancellations
The value of the RecordCancellations option determines whether term cancellations are recorded
during computation. If set to True, a cancellation history is written to the options section of the
DAEObject given as argument to CancelTerms. Note that it is not written to the returned DAEObject.
The command ShowCancellations (Section 3.12.7) can then be used to visualize the history list. If
set to False, no history list is recorded. The default setting is RecordCancellations −> True.
If you cancel terms in different levels, the history list of the first level will be recorded only.