Hi all,

I have one of the classic problems. Saving output from a regression to a matrix. I tried to search, google etc but couldn't find a solution.
I am running several regressions. It is actually a command called traj. A Stata plugin written i C. Downloadable from https://www.andrew.cmu.edu/user/bjones/index.htm In short it performs longitudinal finite mixture models. I am running several models, trying to find the best combination of trajectories and polynomials. I am saving BIC, AIC, etc in a matrix. I want to save another result as well. See below.

Dataset, it is actually 28 time points and values. Showing the first 5 values for 5 patients. Each timepoint ( time_n ) measures a organ failure score ( sofa_resp_orig_n ) in 660 critically ill patients.
Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float(sofa_resp_orig_1 sofa_resp_orig_2 sofa_resp_orig_3 sofa_resp_orig_4 sofa_resp_orig_5 time_1 time_2 time_3 time_4 time_5)
2 1 0 0 0 1 2 3 4 5
2 3 2 3 2 1 2 3 4 5
2 2 . . . 1 2 3 4 5
2 . . . . 1 2 3 4 5
2 2 1 0 0 1 2 3 4 5
end
Here is my problem.


Code:
* Example generated by -dataex-. To install: ssc install dataex
clear

// Setting polynomials and groups.
local polynom 3
local groups 6

// Creating matrix for later saving of results. This part is run once only.

// Creating matrix
local maxnum: display `polynom'^`groups' +1
display `maxnum'
local columns `groups'
matrix a = J(`maxnum',6,.)
matrix group = J(`maxnum',`columns',.)




timer clear
timer on 1
// Here I am running the code. I am running it several times with different starting points (from different combinations of polynomials.
//  Saving the matrix to excel every time I have run a number of iterations.
// This is because the regression sometimes does not converge and Stata freezes. I do not want to do it all from the first combination
// if this happens. 

    // State polynomials, number of groups (trajectories), maximum iterations (before saving to excel), which combination of
    // groups and polynomials to start from.
local polynom 3
local groups 6
local maxiter 2
local iter_start 1

// Setting variable list for traj command
local first "sofa_resp_orig_1"
local connect "-"
local second "sofa_resp_orig_28"
local maxnum: display `polynom'^`groups'


// Setting up matrix columns and naming them
matrix colnames a = "Groups" "Polynomials" "BIC(N)" "BIC(panels)" "e(AIC)" "e(ll)"
local bicn: display -10^99
local bicp: display -10^99
local aic: display -10^99
local e(BIC_N_data): display -10^99
local e(BIC_N_subjects): display -10^99
local e(AIC): display -10^99


// Filling up matrix with the possible combinations of polynomials. So I can start over at a specific combination later.
matrix b = J(`maxnum',6,.)
local i 1
forvalues a = 1/`polynom' {
    forvalues b = 1/`polynom' {
        forvalues c = 1/`polynom' {    
            forvalues d = 1/`polynom' {    
                forvalues e = 1/`polynom' {
                    forvalues f = 1/`polynom' {    
                        matrix b[`i',1] = `a'
                        matrix b[`i',2] = `b'
                        matrix b[`i',3] = `c'
                        matrix b[`i',4] = `d'
                        matrix b[`i',5] = `e'
                        matrix b[`i',6] = `f'
                        local i `++i'
                                    }
                                }
                            }
                        }                
                    }
                }        

// Extracting polynomial order to traj command
forvalues a = 1/`maxiter'{
local aa = b[`iter_start',1]
local bb = b[`iter_start',2]
local cc = b[`iter_start',3]
local dd = b[`iter_start',4]
local ee = b[`iter_start',5]
local ff = b[`iter_start',6]


// Running the traj command.
    quietly traj, var(`first'`connect'`second') indep(time_1-time_28) model(cnorm) min(0) max(4) order(`aa' `bb' `cc' `dd' `ee' `ff' )
    
    // Saving output to matrix
    matrix a[`iter_start',1]= e(numGroups1)
    matrix a[`iter_start',2]= `aa'`bb'`cc'`dd'`ee'`ff'
    matrix a[`iter_start',3]= e(BIC_N_data)
    matrix a[`iter_start',4]= e(BIC_n_subjects)
    matrix a[`iter_start',5]= e(AIC)
    matrix a[`iter_start',6]= e(ll)    
    
// !! here is my problem !!   See below for description.
    

    local iter_start `++iter_start'
}
    
timer off 1


di "`maxiter' iterations, total time"
timer list 1

// Saving matrix a (results summary) to excel in case Stata freezes.
cd "whereever/- Renal 5gr 3 poly"
putexcel set `first'`connect'`second'gr`groups'poly`polynom'_`maxiter'_`iter_start' , replace
putexcel A1 = matrix(a), names

end
In the code above, you can see where I say my probem is. The traj command in ereturn gives amongst other things a matrix of the percent of patients in each trajectory (e(groupSize1)). I want to save these numbers.
e(groupSize1) is a matrix with one row and n columns. n is the number of trajectories estimated (6 for 6 groups/trajectories, 5 for five groups/trajectories etc).

SO I want to:
1. I want to be able to run a number of traj estimations.Starting at a given combination of trajectories and poynomials.
2. Save all results (BIC, AIC etc) to matrix a which is done in the code above. 1-2 works fine.

3. I want to save e(groupSize1)for each estimation and add this matrix to matrix a. This I can not do.
I could easily save e(groupSize1) to a matrix ( matrix groupsize = e(groupSize1)) But either matrix groupsize needs to be increased with ++i for each new estimation, and last in the code appended with matrix a.
Or, perhaps better, be added to matrix a after each run. But I then need to append matrix a with a number of columns (corresponding to the columns in e(groupSize1) every time.

Dummy code (for insertion in the code where my problem is:
matrix groupsize = e(groupSize1)
matrix a[`iter_start',7]= groupsize

This obviously does not work, I get a matrix configuration error. I get this even if I increase matrix a to be able to contain more columns. Any suggestions how to add e(groupSize1)to matrix a for every iteration of traj?

Hope I am making myself somewhat clear...


Best regards,
Jesper