subplots are all in the same figure (a.k.a. window), by definition, so it's not clear exactly what you want to see.
You are seeing the last plot in its own figure (the most recent figure created right after you run the code), but the other plots should still exist, in another figure (perhaps underneath the most recent figure).
x=linspace(0,10);
a=x+1;
b=x.^2+x+1;
c=x.^3++x.^2+x+1;
d=x.^4+x.^3++x.^2+x+1;
plot(x,a)
grid
hold on
plot(x,b)
grid
hold on
plot(x,c)
grid
hold on
hold on
figure
plot(x,d)
grid
hold off
To use subplots instead:
figure()
subplot(2,2,1)
plot(x,a)
grid
hold on
subplot(2,2,2)
plot(x,b)
grid
hold on
subplot(2,2,3)
plot(x,c)
grid
hold on
subplot(2,2,4)
plot(x,d)
grid
hold off
