We need to lay down the elements of the matrix. Erring error C2110: +:

I need to lay down the elements of the matrix.
Errors error C2110: +: Two indexes 
Please.
for(int i = 3 ; i< G ; i++) { for(int j = 1 ; j <7; j++) { Matrix[i][j] = (Matrix[i1,j]) + Matrix[i1,j]; }
}

Flaw in the line
Matrix[i][j] = (Matrix[i1,j]) + Matrix[i1,j];
Specifically, you're not using the operator properly.
[]
Because you've got masses,
Matrix[a]
Come back. IndexNot the meaning.That's why you need to be replaced.
Matrix[i1,j] ; Matrix[i1,j]
♪
Matrix[i1][j] ; Matrix[i1][j]