Matrix with Dynamic size

[Peter Thesling]

I would like to create empty matrixes within mata, whose size is given by a parameter. My program first asks for which tests should be executed and then I create the matrix size accordingly, such that I can save all p-values in one matrix. In particular:

program ...
syntax varlist, POOLED(integer) GROUP_mean(integer) MEDIAN(integer) B(integer) DC(integer)
matrix test = (`pooled'\ `group_mean' \ `median')
local nt = test[1,1]+test[2,1]+test[3,1]
end

mata:
void initialize()
{
st_local("nt")
real matrix pval
pval = J(nt, 1,0)
}

end


However that doesn't seem to work. My suspicion is that J will only take integer numbers as arguments. Is this right or is there other mistakes I am running into?

Thank you.

[Sergiy Radyakin]

My suspicion is that J will only take integer numbers as arguments.

J() wants integer matrix dimensions. You can't have a 2.71 by 3.14 matrix.

is there other mistakes I am running into?

You are running into a different problem. Mata's nt is not initialized. You need something like:

nt=strtoreal(st_local("nt"))

in your Mata portion of the code to transfer the value of the nt visible in Stata to Mata.

All matrices are dynamic, in a sense that you can always do (for conforming matrices A and B)

A=A,B

And the matrix A will be growing in size. No need to do anything fancy.

I would like to create empty matrixes within mata

Empty matrix has dimensions 0x0:

mata A=J(0,0,.)

J() will create a matrix of given dimensions. You can initialize it to any value. Missings and zeroes are popular choices.

Best, Sergiy Radyakin