We introduce a modification of the PyUltraLight code that models the
dynamical evolution of ultralight axionlike scalar dark matter fields. Our
modified code, PySiUltraLight, adds a quartic, self-interaction term to reflect
the one which arises naturally in axionlike particle models. Using a particle
mass of $10^{-22}~\mathrm{eV}/\mathrm{c}^2$, we show that PySiUltraLight
produces spatially oscillating solitons, exploding solitons, and collapsing
solitons which prior analytic work shows will occur with attractive
self-interactions. Using our code we calculate the oscillation frequency as a
function of soliton mass and equilibrium radius in the presence of attractive
self-interactions. We show that when the soliton mass is below the critical
mass ($M_c = \frac{\sqrt{3}}{2}M_{\mathrm{max}}$) described by Chavanis
[arxiv:1604.05904] and the initial radius is within a specific range, solitons
are unstable and explode. We test the maximum mass criteria described by
Chavanis [arxiv:1604.05904] and Chavanis and Delfini [arxiv:1103.2054] for a
soliton to collapse when attractive self-interactions are included. We also
analyze both binary soliton collisions and a soliton rotating around a central
mass with attractive and repulsive self-interactions. We find that when
attractive self-interactions are included, the density profiles get distorted
after a binary collision. We also find that a soliton is less susceptible to
tidal stripping when attractive self-interactions are included. We find that
the opposite is true for repulsive self-interactions in that solitons would be
more easily tidally stripped. Including self-interactions might therefore
influence the survival timescales of infalling solitons.
