This work addresses nonperturbative effects in both matrix models and
topological strings, and their relation with the large-order behavior of the
1/N expansion. We study instanton configurations in generic one-cut matrix
models, obtaining explicit results for the one-instanton amplitude at both one
and two loops. The holographic description of topological strings in terms of
matrix models implies that our nonperturbative results also apply to
topological strings on toric Calabi-Yau manifolds. This yields very precise
predictions for the large-order behavior of the perturbative genus expansion,
both in conventional matrix models and in topological string theory. We test
these predictions in detail in various examples, including the quartic matrix
model, topological strings on the local curve, and Hurwitz theory. In all these
cases we provide extensive numerical checks which heavily support our
nonperturbative analytical results. Moreover, since all these models have a
critical point describing two-dimensional gravity, we also obtain in this way
the large-order asymptotics of the relevant solution to the Painleve I
equation, including corrections in inverse genus. From a mathematical point of
view, our results predict the large-genus asymptotics of simple Hurwitz numbers
and of local Gromov-Witten invariants.Comment: 50 pages, 24 figures, JHEP3.cls; v2: added references, added
discussion on Painleve I, final version for CNT