Patent ID: 7113112

Claim:
A method of compressing data comprising: (a) providing a string to be compressed; (b) selecting an approximately optimal PPM model for the string by: (i) providing an objective function that measures the desirability of proposed PPM models; (ii) starting with i=1, determining an order-i PPM model for the string; (iii) determining an order-(i+1) PPM model for the string; (iv) using the objective function to determine whether the order-(i+1) PPM model is more desirable than the order-i PPM model; and, (v) if the order-(i+1) PPM model is less desirable than the order-i PPM model, selecting the order-i PPM model as the approximately optimal PPM model for the string; otherwise, increasing the value of i by one, and repeating steps (iv)-(v); (c) using the approximately optimal PPM model to compress the string.