function f = P_norm(FunctionCell)
fnum = size(FunctionCell,1);
p = 250;
f = @(x,y,z) power(FunctionCell{1}(x,y,z),-p);
for i = 2:fnum
f = @(x,y,z) f(x,y,z) + power(FunctionCell{i}(x,y,z),-p) ;
end
f = @(x,y,z) power(f(x,y,z),-1/p) ;
