I'm working on a survival analysis project and, based on previous work of
my colleagues on similar projects, am trying to estimate an AFT model with
a generalized gamma distribution.  When I execute the following code:

>flexsurvreg(timesurv ~ cycles + rcycle + cyctime, dist="gengamma")

I get the following error message:

Error in optim(optpars, minusloglik.flexsurv, t = Y[, "time"], dead = Y[,
 :
  non-finite finite-difference value [4]

I get an almost identical error (a 3 in the brackets instead of a 4) if I
use the dist = "weibull".  But have no problems when I run survreg with
Weibull distribution on the same data.

I've seen some messages about similar errors for other functions, but don't
think the responses apply (at least not in a what I understand).  I tried
setting initial values based on the survreg output values and that didn't
help.  Also, I checked and none of the variables are particularly
well-correlated.

Any idea how to deal with this?

Thanks,

-- 
Brett Close

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