Only check if statement once, or, disable code block after 1 check
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In my ODE_func I have several blocks of code have which are toggle on/off based on the settings of the calculations. Unfortunately Matlab checks the if-statements which controls these blocks every time step, resulting in significant overhead.
Is it possible to only check these if-statements once during the entire calculation, thus disabling the code-block for the entire calculation? Or to rephrase the question, can I tell Matlab some variables are constant during the entire calculation so it doesn't have to keep checking the same if-statement.
Many thanks!
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Risposte (3)
Amit
il 20 Gen 2014
This kind of optimization would really depend on your code. There is no generalization for this (to my knowledge).
If you post the code, or the segment of the code you're interested in, then one can give you suggestions to improve the performance.
3 Commenti
Amit
il 20 Gen 2014
if option1 and option 2 does not turn to 1 simultaneously, then you can reduce the two if statements to if.. elseif.
However I'd think that might have done that already if that was the case.
Also, it surprises me that if statement would such a overhead in the calculations. By any chance, your ODE function is stiff? 'cause ode45 is very slow in those case and you can try ode15s which will be much faster and order of accuracy is still low to medium.
Paul
il 20 Gen 2014
Sounds like persistent variables may one of the solutions here. Persistent means that the variable will still remember its value the next time the function is called.
persistent condition;
if(isempty(condition)) % return true if condition is not initialized yet
%do calculations for check
if(something==true)
condition=true;
else
condition=false;
end
end
if(condition==true)
%do something
else
%do something else
end
3 Commenti
Reema Alhassan
il 12 Giu 2018
hi I need to use persistent in my code but I am getting an error : persistent declaration is only allowed in a function ..
but I didn't need a function do you know how to do that ?
melvin mariadass
il 9 Giu 2022
Matlab records the variables entered in the code file and stores it until the variables are explicitly cleared or deleted during the run, or if the code file contains any external function. when the solver switches between main file and functions, only the variables related to the current file are accessible.
Persistent variables store the varaibles in a function and retains it when the program calls the same function again avoiding the declaration of the variable each time. this is helpful when the function needs to be called multiple times, as persistent variables add higher time overhead. By using nested functions you can avoid the persistent variables.
Global variables are accessible to any function that are or will be called by the main program, time overhead is really high and this type of variable declaration causes buggy code and not a good programing method.
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