Linear APR model

The linear APR model is a pricing model for a Principal Token quoted in underlying. It assumes that the price of the PT is a unit of underlying discounted by a non-compounded implied rate that stays constant during the term. More specifically, is assumes

$$P(t,T) =\alpha(t)\frac{1}{1+r(T-t)}$$

where $\alpha(t)$ is the PT rate, represented in the contracts as ptRate , $T$ is the maturity timestamp and $t$ is the current timestamp.