FEM tools for caculation of nonlinear problems

				function RT = surftri(p,t)
				
				UT  = [t(:,[1,2,3]);
				       t(:,[1,2,4]);
				       t(:,[1,3,4]);
				       t(:,[2,3,4])];
				mqr = [t(:,4);t(:,3);t(:,2);t(:,1)];
				UT  =sort(UT,2);
				
				[foo,ix,jx] = unique(UT, 'rows');
				vec = histc(jx,1:max(jx));
				
				qx = find(vec==1);
				RT = UT(ix(qx),:);
				mqr= mqr(ix(qx));
				
				v1 = p(RT(:,2),:)-p(RT(:,1),:);
				v2 = p(RT(:,3),:)-p(RT(:,1),:);
				v3 = p(mqr,:)-p(RT(:,1),:);
				
				ix = find(dot(cross(v1,v2,2),v3,2)>0);
				
				RT(ix,[2,3]) = RT(ix,[3,2]);