st: simulate error

[Mark Baerthel <mail2markb@gmail.com>]

clear all

program define mark, rclass

use ".\dta\full.dta"
keep if loan_status =="Fully Paid" | loan_status =="Charged Off"
keep if year == 2010
keep if term ==" 36 months"

sample 5 if grade=="A" , count
sample 5 if grade=="B" , count
sample 5 if grade=="C" , count
sample 5 if grade=="D" , count
sample 5 if grade=="E" , count
sample 5 if grade=="F" , count
sample 5 if grade=="G" , count

summarize ahpr_matured
return scalar mean = r(mean)
return scalar sd   = r(sd
end

simulate pipi=r(mean) pipi2=r(sd), reps(10): mark

ALWAYS GET THIS ERROR !!

. simulate pipi=r(mean) pipi2=r(sd), reps(10): mark
nothing found where name expected
an error occurred when simulate executed mark
r(198);


why ??

thank you so much.
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