Variable ... is undefined on some execution paths

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Federico Avino
Federico Avino 2020-11-30
回答： Walter Roberson 2020-11-30
I'm doing a project in Simulink/Simscape, and it contains a Matlab Function block, which contains the code that must be executed each cycle by the simulator. In this block i need to calculate the discrete derivative of temperature doing (T1-T1_prev)/dt, where T1 is one of the inputs of the block.
In theory, the problem of this methode is the definition of T1_prev at the time 0 of the simulation, so i did an
function y = TCU(u)
%% input
...
time = u(6);
if time <= 0
...
T1_prev = 0;
end
temperature_tank1 = temperatureCheck (T1, T1_prev, Tmax, Tsig, dT_dt_max, deltat);
T1_prev = T1;
y
end
I reported just the parts which i have problems with. In this way matlab says T1_prev is not fully defined due to the lack of an else case, but actually i don't want it, and T1_prev results fully defined, because it's updated in the end of the cycle for each cycle that is not the first. (T1 is updated each cycle too)
How can i solve the problem?
Thank you guys
  2 个评论
John D'Errico
John D'Errico 2020-11-30
Learn to use the debugger? Clearly, even though you think it is always defined, there are some paths where it is not.
Federico Avino
Federico Avino 2020-11-30
Thank you, I know technically it's not fully defined for the compiler (absence of T1_prev in else case), but for the simulation it is defined because the structure of the execution, so the real case, is cyclical. How can I manage to overcome this false error?

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采纳的回答

Walter Roberson
Walter Roberson 2020-11-30
persistent T1_prev
if isempty(T1_prev); T1_prev = 0; end

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