st: mata programming - input type

[Tomáš Houška <xbender@gmail.com>]

Dear Stata list,

I am trying to write this loop (here I give an example in "stata
language", but I am aware that this will never work as mata cannot be
processed within Stata loop):

Example:

levelsof time_period, local(period_id)

foreach period of local period_id {
mata
        //import STATA matrices
	EPSILON = st_matrix("EPSILON_M`period'")
	PRICE   = st_matrix("PRICE_M`period'")
	SHARE   = st_matrix("SHARE_M`period'")
	
	BETA = EPSILON :* ( (SHARE *(1:/PRICE)') )

       st_matrix("BETA`period'",BETA)

end
}

Which means I have several matrices, each marked by period number and
I am trying to perform some operations on them (here I give a
simplified example of my code). I would like to create a mata function
that would take "period_id" as an input (period_id is always in
integer) and process the mata code, resulting in creating new matrix
BETA`period_id'.

So far I have been able to come up with this:
Example 2:

mata
mata clear
void mc_estim(string scalar period) {
	//import STATA matrices
	EPSILON = st_matrix("EPSILON_M`period'")
	PRICE   = st_matrix("PRICE_M`period'")
	SHARE   = st_matrix("SHARE_M`period'")
	
	BETA = EPSILON :* ( (SHARE *(1:/PRICE)') )

        st_matrix("BETA`period'",BETA)
	}
end
* run mata function with a selected input
mata mc_estim(534)

But I am not sure how to use the "input" in the mata function code (I
expect that the notation is different from Statas local macros....) I
would appreciate any help on this.
Thank you!
T.
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