Index exceeds the number of array elements (2)

I am getting an index error for the code below

tspan=linspace(0,10,100);

init=[5,0]; %=[t,z]

[t,y]=ode45(@(t,y)dsolve(t,y), tspan,init);

plot(t,y)

tn=(y(2)*3/1)

function dx=dsolve(t,y)

dx(1,1)=y(2)*2+y(4)*2;

dx(2,1)=-2*y(1)+3*y(2);

dx(3,1)=y(3)+2*y(1);

dx(4,1)=y(1)+2*y(2)+3*y(3)+4*y(4);

end

output:

Index exceeds the number of array elements (2).

Error in blahjifedfjl>dsolve (line 12)

dx(1,1)=y(2)*2+y(4)*2;

Error in blahjifedfjl>@(t,y)dsolve(t,y)

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 blahjifedfjl (line 5)

[t,y]=ode45(@(t,y)dsolve(t,y), tspan,init);

Answer 1

[Erivelton Gualter]

Hi Ali,

Your dsolve function has 4 states variables: dx(1,1), dx(2,1), dx(3,1), and dx(4,1). Therefore you need an initial variable of size equalt o 4 as weel. Let's say you have init=[5,0, 0, 0];

tspan=linspace(0,10,100);
init=[5,0,0,0]; %=[t,z]
[t,y]=ode45(@(t,y) dsolve(t,y), tspan,init);

plot(t,y)

function dx=dsolve(t,y)
    dx(1,1)=y(2)*2+y(4)*2;
    dx(2,1)=-2*y(1)+3*y(2);
    dx(3,1)=y(3)+2*y(1);
    dx(4,1)=y(1)+2*y(2)+3*y(3)+4*y(4);
end