functions in digit2.i -

             digit2(y0,x0, y,x)  
 
       -or- digit2(y0,x0, y,x,reg)  
     return the index of the zone of the point or points (X0,Y0)  
     in the quadrilateral mesh (X,Y) with the optional region  
     array REG.  The result has the same dimensions as the input  
     X0 and Y0 arrays.  The result is <=0 at points outside the mesh.  
     By default, the zone index is an index into an (M-1)-by-(N-1)  
     array, if X and Y are M-by-N.  However, if the keyword pt= is  
     non-nil and non-zero, the return value is the index into an  
     M-by-N array in which the first row and column are non-existent  
     (like the optional REG array).  

             z0= interp2(y0,x0, z,y,x)  
 
       -or- z0= interp2(y0,x0, z,y,x,reg)  
     return the bilinear interpolate of the function Z(X,Y) at the  
     points (X0,Y0).  The X, Y, and optional REG arrays specify a  
     quadrilateral mesh as for the plm function.  The Z values are  
     specified at the vertices of this mesh, so Z must have the  
     same dimensions as X and Y.  
     Points outside the mesh get the value 0.0, unless the outside  
     keyword is non-nil, in which case they get that value.