st: doubt on Mata using multiple loops

[Gioia de Melo <gioiademelo@gmail.com>]

Hi,

I have problems linking two matrices with for and if.
Matrix X is of n*5, in the first column it identifies firms, columns 2:5
identify firms that are connected to firm in column 1. I need to create a
symmetric matrix A nxn that has 1 in cells between two firms that are
connected.

I run this program but it does not alter A although it does not point any
error:


mata

A=J(20,20,0)

X = st_data(.,.)

for (i=2;i<=cols(X);i++) {
for (j=1;j<=rows(X);j++){
for (i1=1;i1<=cols(A);i1++) {
for (j1=1;j1<=rows(A);j1++){
if (j1==j & i1== X[j,i]){
A[j1,i1]==1
}
}
}
}
}
end

Thank you for your help.

Gioia

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