*! version 1.1.0 PR 26Feb1999. STB-50 sg112.1
program define frac_ext
version 6
/*
	Extract values (e.g. powers, initial values) for individual variables.
	1 = x-variables, 2 = value_string, 3 = name (e.g. init),
	4 (optional) = separator.
	Example: fracext "rhs'" "`init'" init \
*/
local rhs "`1'"
local target "`2'"
local tname "`3'"
local sep "`4'"
if "`sep'"=="" { local sep "," }

unabbrev `rhs'
local rhs `s(varlist)'
local nx: word count `rhs'
local j 0
while `j'<`nx' {
	local j=`j'+1
	local n`j': word `j' of `rhs'
}
quietly {
	tokenize "`target'", parse("`sep'")
	local ncl 0 /* # of comma-delimited clusters */
	while "`1'"!="" {
		if "`1'"=="`sep'" { mac shift }
		local ncl=`ncl'+1
		local clust`ncl' "`1'"
		mac shift
	}
	if "`clust`ncl''"=="" { local ncl=`ncl'-1 }
	if `ncl'>`nx' {
		noi di in red "too many sets of `tname'() values specified"
		exit 198
	}
/*
	Disentangle each varlist:string cluster
*/
	local i 1
	while `i'<=`ncl' {
		tokenize "`clust`i''", parse("=:")
		if "`2'"!=":" & "`2'"!="=" {
			if `i'>1 {
				noi di in red /*
				 */ "invalid `tname'() value `clust`i''" /*
				 */ ", must be first item"
				exit 198
			}
			local 2 ":"
			local 3 `1'
			local j 0
			local 1
			while `j'<`nx' {
				local j=`j'+1
				local 1 `1' `n`j''
			}
		}
		local arg3 `3'

		unabbrev `1'
		tokenize `s(varlist)'
		while "`1'"!="" {
			frac_in `1' "`rhs'"
			local val`s(k)' `arg3'
			mac shift
		}
		local i = `i'+1
	}
* transfer values to $S_*
	local j 0
	while `j'<`nx' {
		local j=`j'+1
		global S_`j' `val`j''
	}
}
end