Nabla cosine
From timescalewiki
Let $\mathbb{T}$ be a time scale and $p \in C_{ld}$ and $-\nu p^2 \in \mathcal{R}_{\nu}$.
$${\hat{\cos}_p(t,s)}=\dfrac{\hat{e}_{ip}(t,s)+\hat{e}_{-ip}(t,s)}{2}$$
Let $\mathbb{T}$ be a time scale and $p \in C_{ld}$ and $-\nu p^2 \in \mathcal{R}_{\nu}$.
$${\hat{\cos}_p(t,s)}=\dfrac{\hat{e}_{ip}(t,s)+\hat{e}_{-ip}(t,s)}{2}$$
