R help - Nov 2015 - Error survreg: Density function returned an an invalid matrix

> Hi, I want to perform a survival analysis using survreg procedure from
> survival library in R for a pareto distribution for a time variable, so I
> set the new distribution using the following sintax:
>
>      library(foreign)
>      library(survival)
>      library(VGAM)
>
>      mypareto <- list(name='Pareto',
>                   init= function(x, weights,parms){
etc.

The survreg routine fits location-scale distributions such that (t(y) - Xb)/s ~
F, where t
is an optional transformation, F is some fixed distribution and X is a matrix of
covariates.  For any distribution the questions to ask before trying to add the 
distribution to survreg are
   - can it be written in a location-scale form?
   - if so, how do the parameters of the distribution map to the location (Xb)
and scale (s).

In fitting data we normally have per-subject location (X b) but an
intercept-only model is
of course possible.

If y is Weibull then log(y) fits into the framework, which is how survreg fits
it.  The
transformation of parameters location and scale parameters for log(y) back to
the usual
Weibull parameterization for y often trips people up (see comments in the
Examples section
of ?survreg).

The log of a Pareto can be written in this form (I think?).  The two parameters
are the
scale a and lower limit b, with survival function of S(x)= (b/x)^a, for x >=
b.  If y =
log(x) the survival function for y is
S(y) = (b/exp(y))^a = exp[-(y - log(b))/(1/a)], which has location log(b) and
scale 1/a.
But even if I am correct the discontinuity at b will cause the underlying
Newton-Raphson
method to fail.

  Terry Therneau