New Matlab user. My equations say I do not have enough inputs. How do I correct this?

tspan = linspace(0,15,201);
y0=[0 15];

[t, y] = ode15s(f,tspan,y0);

function dydt=f(t,y)

dydt(1)=1.57-.00145 *y(1)*y(2);

dydt(2)=7.30-.53*y(1)-.00145*y(1)*y(2);

plot(t,y);

end

Answer 1

[madhan ravi]

 tspan = linspace(0,15,201);
 y0=[0 ;15]; 
 [t, y] = ode15s(@f1,tspan,y0)
 plot(t,y(:,1),'-o')
 hold on
 plot(t,y(:,2),'-ob')
 function dydt=f1(t,y)
 dydt(1)=1.57-.00145 *y(1)*y(2);
  dydt(2)=7.30-.53*y(1)-.00145*y(1)*y(2);
  dydt=[dydt(1);dydt(2)] %added this line to make sure it’s a column vector.
  end

Note:See the function file attached.

Use

[t, y] = ode15s(@f1,tspan,y0)

Instead of

[t, y] = ode15s(f1,tspan,y0)

[madhan ravi]

If something isn’t clear let know. If it solved your problem then please accept my answer.

[madhan ravi]

Did it work? @Alex

[Alex F]

Yes, I see my problem.

[Alex F]

Is there a reason why the @f is used? Also my graph shows blank, that is based on my equation correct?

[madhan ravi]

@f indicates that the function is called with its inputs. I don’t know why you’re getting empty graph but I didn’t have any problem getting the graph.

[Stephen23]

"Is there a reason why the @f is used?"

Because ode15s requires the first input to be a function handle:

https://www.mathworks.com/help/matlab/function-handles.html

https://www.mathworks.com/help/matlab/matlab_prog/creating-a-function-handle.html