[ET Trac] [Einstein Toolkit] #798: allow calculations in parameter assignments in parameter files

[Einstein Toolkit]

#798: allow calculations in parameter assignments in parameter files
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  Reporter:  rhaas        |       Owner:          
      Type:  enhancement  |      Status:  reopened
  Priority:  optional     |   Milestone:          
 Component:  Cactus       |     Version:          
Resolution:               |    Keywords:          
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Comment (by rhaas):

 Nono, not just summed. Arbitrary expressions (see UsersGuide section
 D2.3.2):
 {{{
 · ACCUMULATOR specifies that this is an accumulator parameter. Such
 parameters cannot be set
   directly, but are set by other parameters who specify this one as an
 ACCUMULATOR-BASE. The ex-
   pression is a two-parameter arithmetical expression of x and y. Setting
 the parameter consists of
   evaluating this expression successively, with x being the current value
 of the parameter (at the first
   iteration this is the default value), and y the value of the setting
 parameter. This procedure is
   repeated, starting from the default value of the parameter, each time
 one of the setting parameters
   changes.
 }}}

 Making this not order dependent would require changes to how Cactus parses
 parameter files. Non trivial ones at that since you have to track
 parameter dependency of some sort (assume A refers to B which refers to
 C). The easiest way might be to store the initialization as a string and
 mark a parameter as "not initialized", then on first access of the value
 via ParameterGet() check this flag and evaluate the expression if needed.
 Not sure if that also catches DECLARE_PARAMETERS or if that one uses a
 different mechanism to access values (in FORTRAN its just a common data
 area, so something _is_ different).

 Note that I am emphatically not volunteering to implement this. :-)

-- 
Ticket URL: <https://trac.einsteintoolkit.org/ticket/798#comment:23>
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