function dmm=phitod(phi);
%	phitod(phi) provides grain size in mm,
%	given the phi size.
%	if phi is an array, dmm returns an array
%
%	if (min(size(phi))==1)
%	   maxj=max(size(phi));
%	   for j=1:maxj
%	     dmm(j)=2.^(-1*phi(j));
%	   end
%	end

	dmm=2.^(-1.*phi);