MATLAB: How to use extra time varying discrete inputs in Ode45

input variablesMATLABode45

For example as shown in the function below: Where Ts is the variable with initial value, while Qu is input but it changes with time having specific values defined in the matrix.

function Ts=temp(t,Ts,Qu) Ts=Qu/(1500*4190)-12*10^6/(1500*4190)-11.1*3600*(Ts-20)/(1500*4190);

I am using in this way: Qu=[0 0 0 0 0 0 0 0 21 41 60 75] for j=1:12 Qu=Qu(t); [t,Ts]=ode45(@(t,Ts)temp(t,Ts,Qu),(1:1:12),45) end

But its giving error… please explain how to use inputs with changing time with this example.

Best Answer

function main
Qu=[0 0 0 0 0 0 0 0 21 41 60 75];
[t,Ts]=ode45(@(t,Ts)temp(t,Ts,Qu),(1:1:12),45) 
function dTdt=temp(t,Ts,Qu)
Qu_actual = interp1(1:1:12,Qu,t);
dTdt = Qu_actual/(1500*4190)-12*10^6/(1500*4190)-11.1*3600*(Ts-20)/(1500*4190);
end

Best wishes

Torsten.

Related Solutions

MATLAB: How to correct ode45 errors

First, do not use global variables!

Second, you need to declare your function correctly, and pass the extra parameters to it.

This works (in R2018b):

mdot=0.2;
mass=760;
Cp=2300;
UA=191.66;
Ts=150;
Ti=25;
tspan=[0:10:3000];
T0=25;
[t,T]=ode45(@(t,T) Heatingcoil(t,T,mdot, mass, Ti, UA, Cp, Ts),tspan,T0);
disp('Time(sec)  Temp(deg cel)');
disp([t,T])
figure
plot(t,T);
xlabel('Time(sec)');
ylabel('Temp(deg cel)');
title('Time vs Temp');
function dT=Heatingcoil(t,T,mdot, mass, Ti, UA, Cp, Ts)
dT=(mdot*(Ti-T)+(UA*(Ts-T)/Cp))/mass;
end

See the documentation on Function Basics (link).

MATLAB: Update variables within an anonymous function? (Using ode45 on a discrete set of DE’s)

I guess that temp_dist are your solution variables. Thus your call to ODE45 has to be

[times, T] = ode45(@(time, temp_dist) interpolate(time, A, ...
            int_data, tmax, temp_dist, a, b), ...
            subt, temp_dist0);

where temp_dist0 are your initial conditions for temp_dist.

In this way, ODE45 will automatically update dempdist according to

temp_dist = temp_dist + dt*dTdt

But to be honest:

From what you did in your function "interpolate", I can neither identify what your solution variables for ODE45 are nor how your ODEs you are trying to solve look like.