The coherent Ising machine (CIM) enables efficient sampling of low-lying energy states of the Ising Hamiltonian with all-to-all connectivity by encoding the spins in the amplitudes of pulsed modes in an optical parametric oscillator (OPO). The interaction between the pulses is realized by means of measurement-based optoelectronic feedforward which enhances the gain for lower-energy spin configurations. We present an efficient method of simulating the CIM on a classical computer that outperforms the CIM itself as well as the noisy mean-field annealer in terms of both the quality of the samples and the computational speed. It is furthermore advantageous with respect to the CIM in that it can handle Ising Hamiltonians with arbitrary real-valued node coupling strengths. These results illuminate the nature of the faster performance exhibited by the CIM and may give rise to a new class of quantum-inspired algorithms of classical annealing that can successfully compete with existing methods.Introduction. The Ising model, originally developed for the description of phase transitions in magnetic materials [1], is a pillar of many branches in science. Its applications range from quantum field theory [2] and quantum gravity [3] to economics [4] and machine learning [5]. The model is defined by the Hamiltonianwhere J i j = J ji , J ii = 0. The spin variable σ i can be a quantum operator or a number, continuous or discrete. In this paper we are interested in the classical discrete case, σ i = ±1. The goal is to find the configurations of spins which realize or approach the global minimum of the Ising Hamiltonian (1). This is an NP-hard problem, meaning that the number of operations needed to find the exact solution grows exponentially with the size of the spin system [6]. However, there exists a variety of classical algorithms to find an approximate solution [7][8][9][10].Recently, the Ising problem has been approached using noisy intermediate-scale quantum (NISQ) devices. One example is the D-Wave quantum annealer based on superconducting qubits. However, it has a shortcoming associated with low connectivity: each physical qubit in the D-Wave chimera graph architecture is connected to only eight others. Therefore each logical spin must be embedded in multiple physical qubits to model the fully connected Hamiltonian (1), resulting in a significant overhead [11].