How declare a variable only once in a matlab function block and then use the previous value the nex time the function is used?

I am using the matlab function block in simulink. I need it to continuously read its inputs and change its outputs. The problem is that I must declare my start position as zero. Then my function runs and increments as desired. THEN it seems to enter the function again and reset to zero (as it would). I need to declare the variable to zero the very first time through the function then all times after use the value that it generated before. See code below:

function y = fcn(sEMG5,sEMG6)
%#codegen

% %set original servo positions to zero
% servo2=0;
% servo3=0;
% servo4=0;
% servo5=0;

%incrememt servo position when threshold is met
if sEMG5 > 150
    servo2 = servo2+3;

elseif sEMG6 > 150
    servo2= servo2-3;

end

%keep servo position in allowable range
if servo2 > 180
    servo2 = 180;

elseif servo2 < 0
    servo2 = 0;

else
    servo2=servo2;

end

y = servo2;

So my problem is how to declare servo2 as zero once and then use the value that y was all successive times through. Thanks!

Answer 1

[Ryan Livingston]

You could also use a persistent variable inside your MATLAB function block:

function y = fcn(sEMG5,sEMG6)
%#codegen

persistent servo2;

% set original servo positions to zero the
% first time this function is invoked
if isempty(servo2)
  servo2=0;
end

% Use servo2 here
...

[Daniel Sluder]

Thanks. My colleagues want to keep the simulink model as simple as possible

[subhahsay shetty]

what if we want to initialize and then update the values. Can we do that??

Answer 2

[Anthony Poulin]

Is it possible for you to have one more input and one more output? What I suggest is to do like the image below:

You do not work with a variable but with an input (u2) that you update and affect to the output (y2). With a unit delay you have your output, in input the next simulation step u2(z) = y2(z-1). (You configure your unit delay with the initial value to 0)

[Daniel Sluder]

I think this is great!