What is t? The column index? What do you mean by "store"? They're already stored. You stored x in C2, and y in N2, and z in P2 (not sure why the names don't match though, like why C2 is x1,x2,x3... instead of c1,c2,c3,...). Anyway, you can send those to your function -- go ahead and plot them if you want - just call plot().
for col = 1 : length(C2)
result(col) = MyFunction(C2(col), N2(col), P2(col));
end
% Now you have the results.
% Plot the results if you want
plot(result, 'b*-');
grid on;
% Save figure if you want
export_fig(......
