Why doesn't this MATLAB loop plot y values correctly?

[j-lee00]

for x = 1:15

if x < 5
y = 2*x - 5;

elseif 5 < x <10
y = 4*x;

elseif 10< x <15
y = x*x;

end;

end;

plot(x,y)

Why doesn't this work?

 

[Dr Transport]

no equal signs, you are leaving out 5, 10 and 15 right off the bat.