# I need help for a very simple function in Matlab

1 vue (au cours des 30 derniers jours)
Özgür Akpinar le 16 Mar 2014
In the picture a part of my simulink model is shown. It works like this:
"Data" is what is sent from serialport. "Status" is 1 when there is data on serialport and 0 when there is not any data sent.
When I start simulation, if there is data sent "Data" has the value of it. When there is not any data sent "Data" sends 0 as output.
What I want it to do is "If there is any data, give "y" the value of sent data. If there is no data sent keep "y" as the previous value"
So I added my own User Defined Function
function y = fcn(u,x)
if (x == 0)
y = y;
else
y = u;
end
end
But this gives me the error says "y" is not defined. How can I achieve this simple solution wiht or without any user defined function? Can somebody, please, figure it out? Thanks in advance
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### Réponses (1)

the cyclist le 16 Mar 2014
You have not input the previous value of y to fcn(), so at the line
y = y;
the value is unknown. You need something like
function y = fcn(u,x,y0)
if (x == 0)
y = y0;
else
y = u;
end
end
where y0 is the prior value of y.
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