Recursive type equation solution in simscape

Hello everybody, I am new in this community and have a related question. I have following code written in simscape. This is compiled ok as it is prepared in an existing block code. But its not working well. Infact I want to calculate fio2 and then assign its value to qo2 for the next timestep calculation. All the time i get qair = 0 and qo2 = 2.

variables (Access = private , ExternalAccess = observe)

qair = 1 % air flow

end

Parameters (ExternalAccess = observe)

fio2 = 2 %chamber o2

end

intermediates

qo2 = fio2

end

equation

fio2 == qair + qo2

end

Answer 1

[Yifeng Tang]

Feels like you are trying to use Simscape like MATLAB :p, by considering how to use iterations to do the numerical integration. If I understand your intention correctly, you governing equation for this block is

or

and fio2 is just there to record the integral from last time step.

If so, you can get rid of fio2 totally and define the equation as

der(qo2) == -qair

or

qo2.der == -qair

And, add qo2 to the variable list. The initial condition can be set in the block in the variable tab.