Need assistance with incorrect output in plot.

Hi all. I am working on a class project that takes a set of four first order equations and integrates them into a plot. The plot should appear as this below but my graph is totally different and I am not sure what is causing the issue. Can anyone point out where I am going wrong? I am including my full code below. Thanks in advance

%% Creating custom R-K Integrator
clear
clc
dt=0.0001  %0.01 sec was used initially, 
x_vect=[0,0,0,0]; %Initial Conditions
t_span=[0:dt:2];
npoints=length(t_span);

x_dot = @deriv
t0=0;
t(1)=t0;
x_answer(1)=x_vect(1,4);% Initialize answer vector.
for i=1:npoints
    t(i+1) = t(i)+dt; %update t, this value will not be used until next iteration.
    x_vect = integ(x_vect,x_dot,t(i),dt);
    x_answer(i+1)=x_vect(1,4);
    t0=t(i);
 
end
plot(t,x_answer)

function out=integ(x_vect,x_dot,t,dt)  %fourth order runge kutta 
%out=x_vect+x_dot*dt;
k1=x_dot(t,x_vect)*dt;   
k2=x_dot(t+dt/2,x_vect+k1/2)*dt;
k3=x_dot(t+dt/2,x_vect+k2/2)*dt;
k4=x_dot(t+dt,x_vect+k3)*dt;
out=x_vect+1/6*(k1+2*k2+2*k3+k4);
end


function out=deriv(t,y_init) 

    out(1) = y_init(2);
    out(2) = y_init(3);
    out(3) = y_init(4);
    out(4) = -206*y_init(4)-1341.4*y_init(3)-848.4*y_init(2)+60000;
end

[darova]

Please show original equation

[Sean Sweeney]

[Sean Sweeney]

this is the 4th order DE we were given which should output the above graph. However my code it outputing a drastically different plot

[darova]

what is x_dot?

[darova]

@Sean Sweeney

x_dot according to my reacher is supposed to represent the derivitive.

Answer 1

[darova]

Try to change this part

x_answer = zeros(npoints,4);    % preallocate answer vector
x_answer(1,:) = x_vect(1,4);    % Initialize answer vector.

And this part inside for loop

x_answer(i+1,:) = x_vect

[Sean Sweeney]

x_dot = @deriv

t0=0;

t(1)=t0;

x_answer = zeros(npoints,4);

x_answer(1,:) = x_vect(1,4);

for i=1:npoints

t(i+1) = t(i)+dt; %update t, this value will not be used until next iteration.

x_vect = integ(x_vect,x_dot,t(i),dt);

x_answer(i+1,:) = x_vect

t0=t(i);

end

The bold is what I updated from the original code, but it just ran forever until I manually ended the script. Was this the change you were suggesting?