Write ado command with function defined on Mata

[Xiduo Chen]

I am writing an ado file and I use structures like:
program define XX, eclass
myfunction()
ereturn matrix V = `V'
end


mata:
myfunction(
calculate V
st_matrix(`V', v)
)
end

I use trace and it tells me that ereturn matrix V = __000003 invalid syntax
I use -ereturn post `V' before, but it gives back matrix __000003 not found. (but matrix V existed if I use matrix list V instead)
I think I already changed the calculated V into matrix in st_matrix. Do I need mat `V' = e (V) somewhere?

Thanks!

[JanDitzen]

You need to declare the variables you are returning correctly. The code should look like:

program define XX, eclass
tempname V
mata myfunction("`V'")
ereturn matrix `V'
end

mata:
function myfunction(string scalar VName)
real matrix v_int
v_int = rnormal(10,10,0,1)
st_matrix(VName,v_int)
end

In the Stata program you create a temporary name V, which is then passed to the mata program. Within the mata program you create/do calculations with the real matrix v_int, which is then passed to Stata using st_matrix().

[Xiduo Chen]

Thanks a lot! That partially solved my problem.
The trace told me that I have conformability error when I use ereturn post V. (I am sure V is really a matrix by listing it and I also tried to transpose it into column vectors)

[Xiduo Chen]

It seems I need to change the name and use column vector