function v = contvec(zmin,zmax)
% v = contvec(zmin,zmax)
% computes a suitable vector of contour
% intervals, given zmin and zmax
zdif = zmax - zmin;
lzd = floor(log10(zdif));
cdif = 10^(lzd-1);
s = 30;
cdif = cdif/2;
while s > 15 
   cdif = 2*cdif;
   cmin = cdif*ceil(zmin/cdif);
   cmax = cdif*floor(zmax/cdif);
   v = [cmin:cdif:cmax];
   s = length(v);
end;
