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runge-Kutta problem command ode45

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I try to solve an equation with the command ode45 b ut I have an error, this is my code:
tspan = [0 5];
y0 = 100;
Q = 30, b = 0.2;
[t,y,x] = ode45(@(tspan,y,x) Q-b*x*y, t, y0);
plot (t,y,x,'-o')
and the error:
Q =
30
Not enough input arguments.
Error in rungrkutta_y>@(tspan,y,x)Q-b*x*y (line 4)
[t,y,x] = ode45(@(tspan,y,x) Q-b*x*y, t, y0);
Error in odearguments (line 90)
f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
Error in ode45 (line 115)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in rungrkutta_y (line 4)
[t,y,x] = ode45(@(tspan,y,x) Q-b*x*y, t, y0);
how can I solve it?

Accepted Answer

Star Strider
Star Strider on 1 Mar 2021
I have no idea what you want to do, or what ‘x’ and ‘y’ are.
This will get you closer to an actual result:
tspan = [0 5];
y0 = [100; 0];
Q = 30;
b = 0.2;
[t,y] = ode45(@(t,y) [y(1); Q-b*y(1)*y(2)], tspan, y0);
figure
plot (t,y,'-o')
.
  4 Comments
Star Strider
Star Strider on 1 Mar 2021
As always, my pleasure!

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More Answers (1)

Stephan
Stephan on 1 Mar 2021
tspan = [0 5];
y0 = 100;
Q = 30;
b = 0.2;
[t,y] = ode45(@(t,y)Q-b*t*y, tspan, y0);
plot (t,y,'-o')

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