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From Phil Steitz <>
Subject Re: [math] Questions regarding probability distributions
Date Wed, 13 Oct 2004 11:59:11 GMT wrote:
>>Some may disagree with that definition (really amounts to a convention on
>>how to handle vacuuous products); but I think that I agree with you.
>>Unless others object, I will consider this a bug and make the change.
>>Thanks for pointing this oddity out. Would you mind opening a bugzilla
>>ticket to track this?
> Fixed that.


> Well, the problem is this: If I need to create some custom discrete 
> distribution that doesn't take on integer values, what interface should I 
> implement? With your model I have no choice but use the 
> ContinuousDistribution interface even though the distribution *isn't* 
> continuous. Does that make sense?

Can you provide a practical example of this?  IIUC, what you are really 
arguing for is changing the int's in the DiscreteDistribution interface to 
doubles. This has the advantage of greater generality but makes it 
slightly less convenient for implementors of the most common discrete 
distributions, where the values are integers.

> You're right that the domain of every discrete distribution could be mapped 
> into the integers, but then there should be some mechanism for internalizing 
> this mapping for a particular distribution. Every discrete distribution 
> should have a reference to a Domain object that provides a method for mapping 
> every object of the set into the integers. Using such a scheme you could keep 
> separate interfaces for discrete and continuous distributions. (Actually, the 
> continuous distributions could have a Domain object too).

Hmm, one problem that I am now seeing is in computing moments of "mapped" 
discrete distributions. Something like what you are describing above will 
be necessary.  So...if there are practical examples out there, I am 
beginning to think that we need to either a) change the ints to doubles in 
DiscreteDistribution or b) support "value mapping" in some systematic way.


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