st: Mata order() indeterminate

[brendan.halpin@ul.ie (Brendan Halpin)]

I'm checking a simulation in Mata, and find that setting the seed to the
same value does not yield the same results on repeated runs. I've
tracked it down to the use of -order()- to sort a matrix, where there
are many ties. It appears that -order()- brings in indeterminacy in
dealing with ties, but from somewher other thanq the random-number system.

This snippet illustrates the issue:

mata:
x = range(1,10,1)
y = runiform(10,1):>0.5

for (i=1; i<=20; i++) {
  rseed(12345)
  x, x[order(y,1),]
}
end

Though x is unchanged, and the seed is set to the same value at each
pass, x[order(y,1)] changes. 

While this is disturbing, I presume it is consistent with Stata policy
with regard to sorting indeterminacy. 

How do I get repeatable sorting in this context?


Regards,

Brendan
-- 
Brendan Halpin, Head of Department, Sociology, University of Limerick, Ireland
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