B.2 Tips for Making Code Run Faster.

Here are some ways of improving the execution speed of Octave programs.

• Avoid looping wherever possible.
• Use iteration rather than recursion whenever possible. Function calls are slow in Octave.
• Avoid resizing matrices unnecessarily. When building a single result matrix from a series of calculations, set the size of the result matrix first, then insert values into it. Write

            result = zeros (big_n, big_m)
            for i = over:and_over
              r1 = ...
              r2 = ...
              result (r1, r2) = new_value ();
            endfor
       

  instead of

            result = [];
            for i = ever:and_ever
              result = [ result, new_value() ];
            endfor
       

• Avoid calling eval or feval whenever possible, because they require Octave to parse input or look up the name of a function in the symbol table.

  If you are using eval as an exception handling mechanism and not because you need to execute some arbitrary text, use the try statement instead. See The try Statement.

• If you are calling lots of functions but none of them will need to change during your run, set the variable ignore_function_time_stamp to "all" so that Octave doesn't waste a lot of time checking to see if you have updated your function files.