st: unobserved heterogeneity as a fn of the X's in hazards

[Enrique Seira <eseira@stanford.edu>]

Hi, I am fitting a weibull hazard with streg. My problem is that I do not 
know how to introduce unobserved heterogeneity which is a fn of the x's. 
Do you know of any user written program that does this?
Thanks,
Enrique
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