functions in bowtie.i -

             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.  

             nbow, map  
          or nbow, file  
          or nbow, rt, zt  
          or nbow, rt, zt, ireg  
 
     prints information about topological oddities in a mesh.  
     MAP is a bowtie map as returned by the bowtie function.  
     FILE is a binary file containing rt, zt, and ireg arrays.  
     RT, ZT and IREG are 2-D arrays defining a quadrilateral mesh.  
     The information printed includes the zone index (corner with  
     the largest indices) of zones which are concave (boomerangs)  
     or bowtied, and of zones with negative area.  You can set  
     the global variable nbow_negative to 1 to reverse the default  
     sense of positive area.  By default, only the first 10 zones  
     in each category are printed; use the all=1 keyword argument  
     to print a complete (and maybe very long) list.  

             nbow_negative  
 
     default value is 0  
     set to 1 to reverse the sense of positive area for the nbow function