Why is "hold on" not working?

I am trying to plot multiple helices on 1 graph but I cannot seem to figure it out. Below is my code...

clc;
clear all; 
close all;

n = input('number of turns'); 
a = input('radius');
P = input('pitch angle');

t = 0:pi/50:n*2*pi;
b = a*a*tan(P); 
x = a*sin(t);
y = a*cos(t);
z = b*t; 

r = 5:pi/50:n*2*pi;
b = a*a*tan(P); 
x2 = a*sin(r);
y2 = a*cos(r);
z2 = b*r; 

figure(1)
plot3(x,y,z, 'red')

hold on; 

figure(2)
plot3(x2,y2,z2, 'blue')

hold off;

Answer 1

[Geoff Hayes]

Julia - are the multiple helices plotted with

 plot3(x,y,z, 'red')

and

 plot3(x2,y2,z2, 'blue')

If so, then they will display on different figures since you are creating a new figure with figure(2). Try changing your code to

figure(1)
plot3(x,y,z, 'red')
hold on; 
plot3(x2,y2,z2, 'blue')

[Image Analyst]

Actually, you can get rid of that call to figure(1) entirely. It's not needed at all.