Changes

==Optimisation==

==Optimisation==

In a long-running calculation, the choice of a good algorithm is essential. Changing to a better algorithm can often provide much better performance gains than is possible with compiler optimisation.

In a long-running calculation, the choice of a good [[algorithm]] is essential. Changing to a better algorithm can often provide much better performance gains than is possible with compiler optimisation.

Programs often obey the 80-20 rule, where 20% of the code accounts for 80% of the CPU usage. Programmers usually do a poor job of guessing as to which 20% of the code is causing performance problems, so before doing any hand optimisation it is crucial to (use a tool to) measure the program performance and identify the hot spots.

Programs often obey the 80-20 rule, where 20% of the code accounts for 80% of the CPU usage. Programmers usually do a poor job of guessing as to which 20% of the code is causing performance problems, so before doing any hand optimisation it is crucial to (use a tool to) measure the program performance and identify the hot spots.