I want to form a connectivity matrix from a vector file:

an N x N symmetric matrix called C with non-zero entries

in C(i,j) when the area labeled with category i shares a border

with the area labeled with category j (assuming all areas

have unique labels). "Connected" means they share a line, not

just a node.

Looking over the structs for topology files, I don't believe that

this information is explicitly stored (correct me if I'm wrong).

Before I get too carried away, has anyone ever done this?

Seems simple: for (i=0;i<Plus_head.n_areas;++i)

for (j=0;j<P_area.n_lines;++j) {

/* must cross line j, returns adjacent category */

k=find_area_which_shares_line(i,j);

c[cat_of_area(i)][cat_of_area(k)]++;

}

If anyone knows a easy way to do this or can suggest

the best src program and/or library functions to use

as a starting point, I would be grateful for a short

reply in private email.

Thanks,

--Darrell