# I need help for a very simple function in Matlab

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Özgür Akpinar on 16 Mar 2014
Answered: the cyclist on 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

the cyclist on 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.