  The IOP model is a quantum mechanical system of a large-$N$ matrix oscillator
and a fundamental oscillator, coupled through a quartic interaction. It was
introduced previously as a toy model of the gauge dual of an AdS black hole,
and captures a key property that at infinite $N$ the two-point function decays
to zero on long time scales. Motivated by recent work on quantum chaos, we sum
all planar Feynman diagrams contributing to the four-point function. We find
that the IOP model does not satisfy the more refined criteria of exponential
growth of the out-of-time-order four-point function.
