An apparatus for processing trading orders, comprising: a central server connectable to a plurality of terminals on which user orders are to be entered. The central server further comprises: communication means for transmitting user orders between said terminals and said central server via a network; first storage means for storing received user orders as an array whose elements define a particular first resource ordered by a particular user; the first storage means is also to be used for storing the resources that may be offered by users for exchange against the first resource ordered; second storage means for storing an array of coefficients each representing the proportion of a particular order that is to be satisfied; processing means for retrieving the orders from the first storage means, calculating an optimized set of values of the coefficients with respect to at least one predetermined, adjustable constraint and at least one predetermined, adjustable criterion, storing the optimized coefficient values in said second storage means; and output means for communicating the processed orders and their respective coefficients.