functions in std.i - z

    zncen(ptcen)  
 or zncen(ptcen, ireg)  


returns zone centered version of the 2-D point centered array PTCEN.  
The result is (imax-1)-by-(jmax-1) if PTCEN is imax-by-jmax.  
If the region number array IREG is specified, zones with region  
number 0 are not included in the point centering operation.  
Note that IREG should have dimensions imax-by-jmax, like  
the input PTCEN array; the first row and column of IREG are ignored.  
Without IREG, zncen(ptcen) is equivalent to ptcen(zcen,zcen).  
Interpreted function, defined at i0/std.i   line 3662