# Periodic function

HI all,

I want to write in sage a `2pi`

periodic even function defined by `f(t) = -t + pi`

, for `t`

in `[0, pi)`

. I already checked Defining a periodic function and defining periodic functions on this plateform, but none of the provided solutions works for me. My main issue is that I need a way to transform any real number `x`

into its unique representative in the interval `[-pi, pi)`

. For that I used `frac`

and `%`

but they both raise errors. Could anyone help me out?

Thanks.