Outputs of the ode45 is not matching with the known results.

Outputs of the ode45 is not matching with the known results.

What I did:

Symbolic expression of the solution is when t = -0.2 we get.

According to ode45 when t=-0.2 we get.

%odefun.m
function dxdt = odefun(t,x)
dxdt = zeros(2,1);
dxdt(1) = 6*x(1)-2*x(2);
dxdt(2) = -2*x(1)+9*x(2);
end

%lscr.mlx
tspan = -1:0.001:0.5;
[t,x] = ode45(@odefun, tspan, [0 ;5]);
[t(801),x(801,1),x(801,2)] %t=-0.2 at 801th row 

I verified the symbolic solution by hand calculations and Phyton. Thus, I probably made a syntax error/misuse or misinterpreted the documentation.

Answer 1

[Alan Stevens]

Use

tspan = 0:-0.001:-1;

to get the correct values for negative values of t.

[Walter Roberson]

Possibly. What needs to be the case is that the first time in tspan needs to be the same as the time that the boundary condition is for. If the boundary condition is for time 0 then Alan's suggestion is the right choice

[Emre Hakan Demirli]

Thank you for explaining.