1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
|
// zebra.cmd
// Evolver command to alternately color string edges black and white
// Usage: Set color1 and color2 to the two colors you want, if the
// default black and white are not suitable. Then run "zebra".
// Programmer: Ken Brakke, brakke@susqu.edu, http://www.susqu.edu/brakke
color1 := white
color2 := black
zebra := {
local ecount,first_e,v_id,zcolor,zinx,e_id;
ecount := 0; // for safety
// Look for valence 2 vertices with same color edges and
// propagate zebra coloring in both directions.
foreach vertex vv where valence==2 and vv.edge[1].color == vv.edge[2].color do
{
first_e := vv.edge[1].oid;
v_id := vv.id;
zcolor := color1;
for ( zinx := 1 ; zinx <= 2 ; zinx += 1 )
{
// follow connected edges
e_id := first_e;
do
{ set edge[e_id] color zcolor;
v_id := edge[e_id].vertex[2].id;
if vertex[v_id].valence != 2 then break;
if vertex[v_id].edge[1].oid == -e_id then
e_id := vertex[v_id].edge[2].oid
else
e_id := vertex[v_id].edge[1].oid;
zcolor := (zcolor == color1) ? color2 : color1;
ecount := ecount + 1;
} while ( (v_id != vv.id) and (ecount <= edge_count) );
if ( v_id == vv.id ) then break; // don't need to go around the other way
// set things up to go around other way next time through the loop.
v_id := vv.id;
zcolor := color2;
first_e := vv.edge[2].oid;
}
} // end valence 2 vertex loop
} // end zebra
|
