The instructions provided to add weights to a graph in MATLAB documentation are as follows:-
A = [0 5 3 0;0 0 1 2; 0 0 0 11; 0 0 0 0];
G = graph(A,'lower');
G.Edges.Weight = [10 20 30 40 50]';
As you can see in this example we have created a graph using an asymmetric adjacency matrix. Using the graph object returned by graph() we can add weights to its edges. for further reading please visit:- Graph Documentation