matlab rand() function does not working at all

For my ANN homework, I want to add noise and plot some curves but I can not add the noise. I have the same result with adding noise or without adding noise. I do research and Ienter image description here have tried transpose of x,y but I still I can not understand where is the problem. Here, it is a little part of my code Thanks for the help!

x = 0.1:0.1:2; y = 2*exp(3*x); plot(x,y,'r--') N = - 0.5 + rand (1,20); y = y + N; figure plot(x,y,'b--') hold on;