Basics of MATLAB and Beyond

The last row needs special treatment (see what happens when you letthe loop run to i = N). On my computer this code took 2.1 seconds toexecute, compared to 2.9 seconds for the simple for loop implementationgiven on page 177. We have saved nearly one second: not much, but ifyou have to repeat the calculation 10,000 times it becomes worthwhile.38.2 M-File Subfunctionsmatlab allows you to put more than one function in a file. If you putmore than one function in a file, the second and subsequent functions aresubfunctions; the first is the main function, or primary function. Theidea is to have a file with the following structure:function dinner = cook(entree,maincourse,dessert)% Get matlab to cook a meal.E = prepare(entree);M = prepare(maincourse);D = prepare(dessert);dinner = [E M D];function output = prepare(course)switch iscourse(course)case ’entree’output = makeentree;case ’maincourse’output = makemaincourse;case ’dessert’output = makedessert;otherwisedisp(’Unknown course: do you really want to eat this?’)endIn this example prepare is the subfunction of the cook function. Whenmatlab encounters the call to prepare, it checks to see if there is asubfunction called prepare in the same file before looking along thesearch path for an m-file called prepare. (Actually before looking alongthe path, it checks for the existence of a private subdirectory first. Seethe helpdesk if this intrigues you.) This means that you can give asubfunction the same name as an existing matlab function. The mainfunction will use the subfunction and any other function will use theother existing function. As is true for single-file functions, subfunctionscannot “see” variables unless you pass them as arguments or declarethem global. Subfunctions are invisible to help, which sees only themain function.c○ 2000 by CRC Press LLC