Apparatus and method of inputting data into an Ising machine. The apparatus may comprise at least one processor to carry out a conversion process to convert an input expression, in a format unsuitable for inputting into an Ising machine, to a suitable format, including creating a dataset of input-output data pairs on the basis of the input expression, deriving a mathematical expression by fitting a first dataset subset to coefficients of an exemplary mathematical expression in the suitable format, and using a second dataset subset, different from the first, to assess whether the derived expression meets a preset quality metric. The derived expression is input to the Ising machine when it is assessed as meeting the metric. The conversion process may be repeated using a different input expression when the derived expression is assessed as failing to meet the metric.