When comparing values to NaN using the relational equals operator (==), MATLAB always returns false. For example, the following code displays false even though it compares NaN to NaN:

x = NaN;
if x == NaN
    disp('true')
else
    disp('false')
end

Instead of using the relational equals operator to compare a variable to NaN, use isnan. For example, the following code displays true:

x = NaN;
if isnan(x)
    disp('true')
else
    disp('false')
end