[R] rgamma question
Icabalceta, Jorge L.
Icabalceta_j at wlf.state.la.us
Fri Feb 6 22:07:07 CET 2004
Sorry to bother you. I am sort of confused with the random number generation
from a gamma distribution. For some reason, if a variable X~gamma(shape,
scale)I have been told that the mean mu can be eithe mu=shape/scale or
mu=shape*scale. Why is that so? This is making me have doubt about the
random generation I am using:
1.- The first variable I have is the precision (h) (the inverse of the
variance)distributed as:
h~gamma((T-2)/2, SSE/2) where T is the number of observations and SSE is the
sum of square errors. How do I draw random number in R with this
information. How do I plug this into
rgamma(n,shape,scale)?
2.- The second variable is L^-1 ~ gamma(T+1, vi-ln(r*)^-1) (please, don't
mind my no explanation for the terms used in the shape and scale
parameters). Again, How do I plug this into
rgamma(n,shape,scale)?
3.- I am having a problem putting the results of each iteration from for(i
1:11000) into samp. For some reason I get 10000 identical values for each
column. What am I doing wrong? To see what the problem is you can try to run
the program. Attached is the data I am using, the program with comments and
without them.
I appreciate your help.
Jorge
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