st: summing across matrices created with a loop

["Schmidt, Nicole" <n.schmidt@neu.edu>]

Hi there,
 
I am using stata to create a pxp matrix for each individual in my 
data set using a loop, and now I want to sum all matrices together. For 
example:
 
forval i=1/`N' {;

  

/* Create a matrix for subject `i' containing value of '1', exposure, and covariates */
mkmat constant `exp' `covs' if obs==`i', matrix(A`i');
matrix list A`i';
/* Transpose matrix */
matrix B`i'=A`i'';
matrix list B`i';
/* Multiplying column matrix B * it's transpose * weight */
matrix C`i'=B`i'*A`i'*W`i';
matrix list C`i';
};
 
Now I want to add all C`i' together to create a pxp matrix that is 
the sum of the C matrix across all individuals in the data. I saw a 
thread about this back in 2007, but it was a suggestion for how to do 
this in mata:

http://www.stata.com/statalist/archive/2007-08/msg00944.html
 
Any advice on how to do this in stata?
 
Thanks,
Nicole


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