[Tutor] Structure of my simulation / monte-carlo

[Dave Angel]

Kent Johnson wrote:
> On Sun, Nov 1, 2009 at 10:47 AM, Vincent Davis <vincent at vincentdavis.net> wrote:
>   
>> Kent Johsnon writes
>> "This class has a lot of responsibilities:
>> - create applicants
>> - create institutions
>> - run a single match
>> - run multiple matches
>> - calculate statistics on the result of multiple matches
>> A principle of object-oriented design is that a class should have a
>> single responsibility. I would break your class up a bit using
>> multiple classes, perhaps."
>> I am trying to do what you recomend, as much as makes sense to me, but that
>> is why I ask the question so I should consider your answer.
>> This is what I hear you saying, (I don't mean to represent them as
>> sub-classes but more how they would operate on each other) Should I consider
>> making Institutions) a subclass of (Make Institutions)? I can't think of
>> anything that would make sense to inherit.
>> class Simulation:
>>     class Create Institutions:
>>         class Institutions:
>>     class create Applicants:
>>         class Applicants:
>>     class Match:
>>     class Multi Match:
>> I add I am thinking
>> class Simulation:
>>     def__init__:(self, results, stats.....repeat..)
>>     def create_applicants():
>>         class Applicants
>>     def creat_institutions():
>>         class Institutions
>>     def one_simulation(): # one or more
>>         create_applicants()
>>         create_institutions()
>>         class Match()
>>         class Results
>>     def repeat_simulation()
>>         repeat one_simulations
>>         class Results
>> After writing this out I now think you are right, more classes.
>>     
>
> Now you are getting too complicated. You don't need to use inheritance
> or nested classes, and you can use simple methods (not classes) to
> create applicants and institutions. You already have Applicant,
> Institution and Match classes that run a single match. Now make a
> RepeatMatch class that uses the Match class to run multiple
> simulations.
>
> Kent
>
>   
I mostly agree with Kent, but I apparently disagree about which classes 
are actually needed.  Think what things will have actual instances that 
will last long enough to be worth formally defining.  So you need 
Applicant, and Institution, and Simulation.  Notice they're all 
singular.  I'm assuming one simulation is a single set of test data, 
with its results.  Then you create as many instances of Simulation as 
you need for comparison purposes, and perhaps keep a list of them.  It's 
not clear that list needs any further structure than the built-in list 
type provides.

You don't need a class for creating an Applicant, that's just a line or 
two in a loop in the Simulation class.  Similarly for Institution.

And if I understand it correctly, you don't need very many different 
methods in Simulation either.  You need the __init__ to save enough 
information to "tag" this particular simulation (call it a label, it's 
probably just a string).  If __init__ is too complex, you may want to 
break it into several phases.  But they'll always be called in direct 
succession, so there may not be any point.  Then you need something that 
triggers an analysis, and something that queries for particular 
results.  That last will then be called from plotting or charting routines.

But you probably don't need anything special for a collection of 
Simulation objects.  A list will probably be fine.

And from what you said earlier, you WILL need function objects, probably 
as parameters to the Simulation constructor.  So each instance of 
Simulation will be given several function objects to specify the 
distribution functions for the parameters to be used when creating 
Applicants and Institutions.

DaveA