Step function

Hi All,

Does the step function work in this model?  I tried to run the
following model but  no result obtained. The computer is hanging and I
killed the job several times. Below is the code.

library(survival)
m.fit=clogit(y~x1+x2+x3+x4, data=ftest)
summary(m.fit)
final<- step(m.fit)

Thanks in advance.