Symbolic mod() does not do what you think it does. And that's a nuisance that has caught me multiple times as well!!
"If a is a polynomial expression, then mod(a,b) finds the modulus for each coefficient."
t is a polynomial in t, equivalent to 1*t + 0 . That is coefficients [1 0]. mod([1 0], 3) is [1 0], so mod(t,3) is 1*t + 0, which is just t.
You have to use something like t - 3*floor(t/3)
