# Coding an if statement within MATLAB function

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Samer ALSAMADI on 20 Jul 2021
Answered: Steven Lord on 20 Jul 2021
Hello,
I am coding a logarithmic quantizer using the MATLAB function block in Simulink. The quantizer has an input u and an output , according to the following equations:  , if and - , if and  (The set of integers).
Given: , u = positive slope ramp signal.
I tried coding the problem myself as follows, but kept receiving the error message: "Variable 'y' is not fully defined on some execution paths.", where y is the quantizer output ( ). I am able to code the above functions for j = 1 for example, but not for j = the set of integers.
My question is, how can I use a while loop within the MATLAB function such that so that I don't receive the error message above?

Steven Lord on 20 Jul 2021
Define y on all the execution paths. Consider this example:
q = myfun(5)
Output argument "out" (and maybe others) not assigned during call to "solution>myfun".
function out = myfun(x)
if x < 1
out = 2;
elseif x > 10
out = 3;
end
end
If x is in the interval [1, 10] then out never gets assigned a value. This is a slightly different error message than the one you're receiving but it's the same cause. In the example above I'd probably add an else statement defining the value out should have if x is neither less than 1 nor greater than 10 or I would assign out that "default" value before the if statement.
Of course, if you're operating on a vector of data the same general principle applies but you need to take into account how if behaves when given a non-scalar condition.