Output of dependent variables in ode solver

Hello, I am using ode15s to calculate the temperature of a room with air conditioning. Now I want to save the used cooling power of the chiller which is calculated as a result of the temperature. How can I add this value to the results? I´ve seen a different complex solutions, but there must be an easier way because in simulink you can just add an output to each variable you want to. Thanks in advance for your answers :)

Answer 1

[Torsten]

As a result from the call to ode15s, you get the temperature TEMP at different times in an array:

[T,TEMP]=ode15s(...)

Now just use a loop over the length of T to calculate cooling power of the chiller:

for i=1:numel(T)
   TEMP_AKTUELL = TEMP(i,1);
   COOLING_POWER_OF_THE_CHILLER(i)= function(TEMP_AKTUELL);
end

Best wishes

Torsten.

Answer 2

[Christian Teicht]

Thank you for your answer Torsten! The problem is, that there are some other factors making it impossible to calculate the cooling power out of the temperature array. That means the function is non invertible :-/ Is there an other possibility?

[Torsten]

The usual way to calculate derived quantities from the solution are:

1. Defining the dependent variable as a solution variable via an algebraic equation which is solved simultaneously by ode15s
2. Using the OutputFcn function 
3. Calling the function routine in which you supply the ODEs after integration has finished and add the dependent variable to the output list

Best wishes

Torsten.

[Christian Teicht]

Thank you for your answer Torsten! I have now programmed the following: main.m: % Main-Programm % Calls ODE-Solver with options to output the dependent variable global kept_values TSpan=0:1:3; Z0=0; options=odeset('OutputFcn', @keepvalues); [tValues ZValues]=ode15s('DE',TSpan, Z0, options); plot(tValues, ZValues, 'b-')

DE.m: function Res=DE(t, Z) global value_to_keep a=1; %m/s² %accelaration dSpeed_dt=a; value_to_keep=a; Res=dSpeed_dt;

keepvalues.m: function status=keepvalues(t,Z,flag) % stores values to a global variable global kept_values value_to_keep

if strcmp('init',flag) kept_values=[]; elseif strcmp('done',flag) 'fertig' else kept_values=[kept_values value_to_keep] end

'called' status=0; %0-->keep integration going, don't stop; 1-->hold integration

My problem is now, how can i pass a value to the function "keepvalues"? If I use a global variable the value doen't fit to the time I requested output (It will take the last one stored).

[Torsten]

Recalculate the value in OutputFcn from the solution y which is supplied in "keepvalues".

Best wishes

Torsten.

[Christian Teicht]

The calculation is quite complex (what I wrote here is just an example), it is not a problem because I can just copy and paste but I think it takes some time for the calculation. Although it works and I'm happy with it!

Thank you very much and have a nice weekend :) Christian