Budget constraint in Radner Sequential Trade Equilibria
In Radner's model each actor starts with an initial endowment, an asset vector $\omega$. You can trade this to any asset portfolio $x$ that has lower or equal value, so
$$x * q \leq \omega * q.$$
Denoting asset trades by $\theta = x - \omega$, you can also express this as
$$
\theta * q \leq 0.
$$