MATLAB: Error : Index exceeds the number of array elements (1).

error

%% Knowns
clear
clc
m_rocket = 95.6; %total mass of rocket (gm)
m_fuel = 15.6; %mass of fuel
f_thrust = 10.7; %force of thrust in N
a_rocket = 0.35; %sqm
c_drag = 0.06; %coefficient of drag
c_dragdown = 0.75; %c drag while falling down due to parachute
g = 9.81; %m/s^2
rho_air = 1.225; %kg/cubicm
drag = 0;
t(1) = 0; %time elapsed
h(1) = 0; %height m/s
v(1) = 0; %velocity m/s
a(1) = -g; %m/s
%% While loop
i=1
h_check = h(1)
t_step = 0.1 %seconds
while h_check >= 0
a(i+1) = ((m_rocket * g) – (0.5 * rho_air*v(i).^2 * c_drag * a_rocket)) / (m_rocket);
v(i+1) = v(i) + (a(i)*t_step);
h(i+1) = h(i) + (v(i)*t_step);
t(i+1) = t(i) + t_step;
h_check = h(i+1);
i = i + 1;
if (m_fuel(i – 1) – 5 * t_step) > 0
m_fuel(i) = m_fuel(i – 1) – 5 * t_step;
f_thrust(i) = f_thrust(1);
else
m_fuel(i) = 0;
f_thrust(i) = 0;
end
a_thrust(i) = (f_thrust(i) – drag) ./ (m_rocket); %a_thrust = acceleration due to thrust
if m_fuel(i) == 0
m_rocket(i) = a(1);
else
m_total(i) = (a_thrust(i – 1) + g);
end
drag(i) = -v(i-1) * abs(v(i-1)) * .0075;
v(i) = v(i-1) + m_rocket(i) * t_step;
h(i) = h(i – 1) + v(i – 1) * t_step + (.5 * m_rocket(i – 1) * t_step .^2)
a(i+1) = ((-m_rocket * g) + (0.5 * rho_air*v(i).^2 * c_drag * a_rocket)) / (m_rocket);
end
figure
plot (t,f_thrust)
title('Time vs Trust')
xlabel('Time')
ylabel('Thrust')
figure
plot (t,a)
title('Time vs Acceleration')
xlabel('Time')
ylabel('Acceleration')
figure
plot (t,v)
title('Time vs Velocity')
xlabel('Time')
ylabel('Velocity')
figure
plot (t,h)
title('Time vs Altitude')
xlabel('Time')
ylabel('Altitude')
Line 81, v(i) = v(i-1) + m_rocket(i) * t_step; , is what's giving me trouble.
(Excuse the mess, I'm pretty new at this.)

Best Answer

Seems like some of your equations are wrong. I changed a few things so the code does not error. Array lengths need to match in equations and indexing cannot exceed or be below zero of the variable being referenced.
m_rocket = 95.6; %total mass of rocket (gm)
m_fuel = 15.6; %mass of fuel
f_thrust = 10.7; %force of thrust in N
a_rocket = 0.35; %sqm
c_drag = 0.06; %coefficient of drag
c_dragdown = 0.75; %c drag while falling down due to parachute
g = 9.81; %m/s^2
rho_air = 1.225; %kg/cubicm
drag = 0;
t(1) = 0; %time elapsed
h(1) = 0; %height m/s
v(1) = 0; %velocity m/s
a(1) = -g; %m/s
%% While loop
i=1;
h_check = h(1);
t_step = 0.1; %seconds
while h_check >= 0
    
    a(i+1) = ((m_rocket * g) - (0.5 * rho_air*v(i).^2 * c_drag * a_rocket)) / (m_rocket);
    
    v(i+1) = v(i) + (a(i)*t_step);
    
    h(i+1) = h(i) + (v(i)*t_step);
    
    t(i+1) = t(i) + t_step;
    
    h_check = h(i+1);
    
    i = i + 1;
    
    if (m_fuel(i - 1) - 5 * t_step) > 0 
        
         m_fuel(i) = m_fuel(i - 1) - 5 * t_step;
         
         f_thrust(i) = f_thrust(1);
         
    else
             m_fuel(i) = 0;
             
             f_thrust(i) = 0;
             
    end
    
    a_thrust(i) = (f_thrust(i) - drag(i-1)) / (m_rocket); %drag(i-1) 
    
    if m_fuel(i) == 0
        
        m_rocket = a(1);%changed m_rocket to not be an array
        
    else
        
        m_total(i) = (a_thrust(i - 1) + g);
        
    end
         drag(i) = -v(i-1) * abs(v(i-1)) * .0075;
         
         v(i) = v(i-1) + m_rocket * t_step;%m_rocket

         
         h(i) = h(i - 1) + v(i - 1) * t_step + (.5 * m_rocket * t_step .^2);%m_rocket
         
         a(i+1) = ((-m_rocket * g) + (0.5 * rho_air*v(i).^2 * c_drag * a_rocket)) / (m_rocket);
         
end
figure
plot (t,f_thrust)
title('Time vs Trust')
xlabel('Time')
ylabel('Thrust')
figure
plot (t,a(2:end))%acceleration is a longer array.
title('Time vs Acceleration')
xlabel('Time')
ylabel('Acceleration')
figure
plot (t,v)
title('Time vs Velocity')
xlabel('Time')
ylabel('Velocity')
figure
plot (t,h)
title('Time vs Altitude')
xlabel('Time')
ylabel('Altitude')
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