Is this a bug of ode function

1 view (last 30 days)
Liu Haoge
Liu Haoge on 6 Mar 2019
Commented: madhan ravi on 7 Mar 2019
I find it's interesting if I change the initial value h0, it will affect the accuracy of "ode45"
close all
tspan=0:0.001:60;
h0=0;%!!!!!!!!!!!!!
[t,h]=ode45(@TankLvl, tspan, h0);
plot(t,h)
xlabel('t')
ylabel('y')
hold on
h2 = h0 + 0.005.*tspan - 0.05.*cos(tspan) + 0.05;
plot(tspan, h2,'r-')
function dh=TankLvl(t,h0)
A=2;
q_in=0.51+0.1*sin(t);
q_out=0.5;
dh=1/A*(q_in-q_out);
end
For example, if I change h0 as:
h0=10;
then the result will be:
It seems that the "ode" function can't deal with the initial value quite well. In order to deal with this issue, I can only set a pseudo initial value h0_pse=0, and use it as the input for "ode", then add the real initial value h0 to the computed h. Shown as following:
h0_pse=0;
h0=10;
[t,h]=ode45(@TankLvl, tspan, h0_pse);
h=h+h0;
  1 Comment
madhan ravi
madhan ravi on 6 Mar 2019
Did you notice something when defining the function input argument?

Sign in to comment.

Answers (1)

SandeepKumar R
SandeepKumar R on 6 Mar 2019
Edited: SandeepKumar R on 6 Mar 2019
It was a tolerance issue. Please define your funtions appropriately. Not a bug in MATLAB
close all
tspan=0:0.1:90;
h0=0;%!!!!!!!!!!!!!
opts = odeset('RelTol',1e-6,'AbsTol',1e-6);
[t,h]=ode45(@(t,z)TankLvl(t,z), [0,90], h0,opts);
plot(t,h,'*')
xlabel('t')
ylabel('y')
hold on
h2 = h0 + 0.005.*t - 0.05.*cos(t) + 0.05;
plot(t, h2,'r')
function dh=TankLvl(t,z)
A=2;
q_in=0.51+0.1*sin(t);
q_out=0.5;
dh=1/A*(q_in-q_out);
end
  1 Comment
madhan ravi
madhan ravi on 7 Mar 2019
also did you notice the OP’s function argument while defining the function?

Sign in to comment.

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by