  In this work, we present a heretofore unseen application of Ising machines to
perform trust region-based optimisation with box constraints. This is done by
considering a specific form of opto-electronic oscillator-based coherent Ising
machines with clipped transfer functions, and proposing appropriate
modifications to facilitate trust-region optimisation. The enhancements include
the inclusion of non-symmetric coupling and linear terms, modulation of noise,
and compatibility with convex-projections to improve its convergence. The
convergence of the modified Ising machine has been shown under the reasonable
assumptions of convexity or invexity. The mathematical structures of the
modified Ising machine and trust-region methods have been exploited to design a
new trust-region method to effectively solve unconstrained optimisation
problems in many scenarios, such as machine learning and optimisation of
parameters in variational quantum algorithms. Hence, the proposition is useful
for both classical and quantum-classical hybrid scenarios. Finally, the
convergence of the Ising machine-based trust-region method, has also been
proven analytically, establishing the feasibility of the technique.
