MATLAB: So whenever I run this program, which is a model of the saturn V rocket going into space. The plot will reset and overlay another plot on top of the other. I don’t know how to explain it well so I hope if you run the program you can see the problem

graphplotplottingwhile loop

close all;
clc;
SATURNVdata = fopen('Rocket.dat','w'); % Opens a file to dump into
dt=10^1;
while dt>=10^-2 % change in dt while loop
    
% Define variables
G = 6.67e-11;
ME = 5.97e24;
RE = 6.37e6;
T_1 = 3.4e7;
ve_1 = 2.58e3;
T_2 = 5.0e6;
ve_2 = 4.13e3;
T_3 = 1.0e6;
ve_3 = 4.13e3;
m0 = 2951000;
% Define initial conditions
y0=0;
v0=0;
m=m0;
t0=0;
t=t0;
% Define initial parameters
y=y0;
a=-(G*ME)/(RE+y)^2+(T_1/m);
v=v0;
fprintf(SATURNVdata,'%f %f %f %f %f\n',t,y,v,a,m); % Dump variables into table
t=t+dt; % time step
    while t<164.6 % ingite stage 1
    m=m-T_1*(dt)/ve_1;
    v=v+a*dt;
    a=-G*ME/(RE+y)^2+T_1/m;
    y=y+v*dt;
    fprintf(SATURNVdata,'%f %f %f %f %f\n',t,y,v,a,m);
    t=t+dt;
    end % empty tank stage 1
    
    m=m-131000; % jettison stage 1
    while t<=167.8 % no thrust


    m=m;
    v=v+a*dt;
    a=-G*ME/(RE+y)^2;
    y=y+v*dt;
    fprintf(SATURNVdata,'%f %f %f %f %f\n',t,y,v,a,m);
    t=t+dt;   
    end
    
    while t<534.6 % ignite stage 2
    m=m-T_2*(dt)/ve_2;
    v=v+a*dt;
    a=-G*ME/(RE+y)^2+T_2/m;
    y=y+v*dt;
    fprintf(SATURNVdata,'%f %f %f %f %f\n',t,y,v,a,m);
    t=t+dt;
    end % empty tank stage 2
    
    m=m-36000; % jettision stage 2
    
    while t<=537.8 % no thrust
    m=m;
    v=v+a*dt;
    a=-G*ME/(RE+y)^2;
    y=y+v*dt;
    fprintf(SATURNVdata,'%f %f %f %f %f\n',t,y,v,a,m);
    t=t+dt;
    end
    
    while t<983.5 % ignite stage 3
    m=m-T_3*(dt)/ve_3;
    v=v+a*dt;
    a=-G*ME/(RE+y)^2+T_3/m;
    y=y+v*dt;
    fprintf(SATURNVdata,'%f %f %f %f %f\n',t,y,v,a,m);
    t=t+dt;
    end % empty tank stage 3
    
    m=m-11000; % jettison stage 3
    
    while t<=1000.1 % no thrust
    m=m;
    v=v+a*dt;
    a=-G*ME/(RE+y)^2;
    y=y+v*dt;
    fprintf(SATURNVdata,'%f %f %f %f %f\n',t,y,v,a,m);
    t=t+dt;
    end
    
    dt=dt*0.1; % change in dt
end
fclose(SATURNVdata); % Closes the file after loop has stopped
load Rocket.dat % Loads the file for creating graphs
%plot of altitude
figure(1)
plot(Rocket(:,1),Rocket(:,2));
title('Altitude')
ylabel('Altitude [m]')
xlabel('time [s]')
hold on
%plot of velocity
figure(2)
plot(Rocket(:,1),Rocket(:,3));
title('Velocity')
ylabel('Velocity [m/s]')
xlabel('time [s]')
hold on
%plot of acceleration
figure(3)
plot(Rocket(:,1),Rocket(:,4));
title('Acceleration')
ylabel('Acceleration [m/s^2]')
xlabel('time [s]')
hold on
%plot of mass
figure(4)
plot(Rocket(:,1),Rocket(:,5));
title('Mass')
ylabel('Mass [kg]')
xlabel('time [s]')
hold on

Best Answer

Look at Rocket(:,1). It starts at 0 and goes up to 1000 by 10. Then it restarts and goes up to 1000 by 1. Then it restarts...by 0.1. Etc. This is because of your while loop with decreasing dt, which generates this repeating series of 0-1000 values.
When you plot these single lines, each of these restarts draws a line back from 1000 to zero and then plots the new values.
Maybe you should keep the results with different dt values in different arrays so you can easily plot 1 series at a time?
Related Question