functions in bowtie.i - b

bowtie
```
map= bowtie(rt, zt)
or map= bowtie(rt, zt, ireg)

returns a "bowtie map" for the quadrilateral mesh defined by
RT, ZT, and (optionally) IREG.  If IREG is present, it should be
an integer array of the same dimensions as RT and ZT; its first
row and column are ignored, otherwise each non-zero element of
IREG marks an existing zone in the mesh.  (An IREG with one fewer
row and column than RT and ZT will also be accepted.)  If IREG
is omitted, every zone is presumed to exist.
The returned MAP is a 2-D integer array with one fewer row and
column than RT and ZT.  It's values have the following meanings:
2   marks a convex zone with positive area
1   marks a concave (boomerang) zone with positive area
0   marks a bowtied zone
-1   marks a concave (boomerang) zone with negative area
-2   marks a convex zone with negative area
-9   marks a non-existent zone
Use the nbow function to print the results.
Interpreted function, defined at i/bowtie.i   line 11

```