MATLAB Programming - A Guide to MATLAB for Beginners and Experienced Users - page 117

function and an initial value and iterates the function a specified number of
times:

function final = iterate(func, init, num)
final = init;
for k = 1:num
final = feval(func, final);

end

Typing iterate('cos', 1, 2) yields the numerical value of cos(cos(1)),
while iterate('cos', 1, 100) yields an approximation to the real num-
ber x for which cos( x ) = x . (Think about it!) Most MATLAB commands that
take a function name argument use feval , and as withall these commands,
if you give the name of an inline function to feval , you should not enclose it
in quotes.

Debugging

In Chapter 3 we discussed some rudimentary debugging procedures. One
suggestion was to insert the command keyboard into an M-file, for instance
right before the line where an error occurs, so that you can examine the
WorkspaceoftheM-fileatthatpointinitsexecution.Amoreeffectiveandflex-
ible way to do this kind of debugging is to use dbstop and related commands.
With dbstop you can set a breakpoint in an M-file in a number of ways, for
example, at a specific line number, or whenever an error occurs. Type help
dbstop for a list of available options.
When a breakpoint is reached, a prompt beginning with the letter K will
appear in the Command Window, just as if keyboard were inserted in the
M-file at the breakpoint. In addition, the location of the breakpoint is high-
lighted with an arrow in the Editor/Debugger (which is opened automatically
if you were not already editing the M-file). At this point you can examine in
theCommandWindowthevariablesusedintheM-file,setanotherbreakpoint
with dbstop ,clearbreakpointswith dbclear ,etc.Ifyouarereadytocontinue
running the M-file, type dbcont to continue or dbstep to step through the file
line-by-line. You can also stop execution of the M-file and return immediately
to the usual command prompt with dbquit .

You can also perform all the command-line functions that we described
in this section with the mouse and/or keyboard shortcuts in the
Editor/Debugger. See the section Debugging Techniques in Chapter 11 for
more about debugging commands and features of the Editor/Debugger.