[R] equation help

[Doran, Harold]

Brendan

It looks like you're working with the 2PL, what are you trying to
estimate exactly? There are a lot of built in psychometric functions
that you might consider using.
 

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Brendan Morse
> Sent: Monday, April 13, 2009 10:54 AM
> To: r-help at r-project.org
> Subject: [R] equation help
> 
> Hi everyone, I am having a bit of trouble correctly 
> structuring an equation in R.
> 
> 
> Here is the equation
> 
> 
> 
> Here is what I thought
> 
> for(i in 1:numItem)for(x in 1:numCat)
> 
>            Ptheta[,i,x]<-(exp(-1.702*a[i]*(theta-b[i,x+1]))
> 
> My problem is that I am not sure how to get it to read the 
> equation as having two indexing points (i and x). Right now 
> it is trying to read it as a matrix, but each value (i and x) 
> are only vectors. Does anyone have any suggestions on how to 
> get R to recognize this? As an example, numItem may = 20 and 
> numCat may = 3 and I am trying to evaluate this over all 
> values of numCat for each value of numItem.
> 
> Thanks,
> Brendan
> 
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