MATLAB by rudra pratap

106
Programming in MATLAB: Scripts and Functions
Executing a function inside another function
Usually, it is a straightforward process, so much so that you do not have to pay any
special attention to it. In the function sol vexf, we used a built-in function, det,
to calculate the determinant of A. We used the function just the way we would
use it at the MATLAB prompt or in a script file. This is true for all functions,
built-in or user-written. The story is different only when you want the function
name to be dynamic, that is, if the function to be executed inside may be different
with different executions of the calling function. 2 In such cases, the actual name of
the function is passed to the calling function through the input list and a dummy
name is used inside the calling function. The mechanism of passing the function
name and evaluating it inside the calling function is quite different from that for a
variable. We explain it below.
A function in the input list
When a function needs to be passed in the input list of another function, the name
of the function to be passed must appear as a character string in the input list. For
example, the built-in function fzero finds a zero of a user-supplied function of a
single variable (see Section 5.6, page 168, for more details) . The call syntax of the
function is fzero (f , x) where f is the name of the function or a function handle
and x is an initial guess. There are several ways in which we can code the function
f and pass it in the input list of fzero. We describe a few common ways of doing
so on an example function:
f(r) = r3 - 32r2 + (r - 22)r + 100.
Fo r on tine help
function .. handl e
Use inline function: We can make f(r) be an inline function (see Section 3.5.1
on page 83 for a detailed discussion) and pass its name to fzero as follows:
fr = inline ('r-3 - 32*r-2 + (r-22)*r + 100');
rO = fzero (fr, 5) ;
Use function file: We can code f(r) in a function file called fu nr.m as follows:
function f = funr(r) ;
% FUNR evaluates function f = r-3 -32 r-2+ (r-22)r+100.
f = r-3 - 32*r-2 + (r-22)*r + 100;
Now we may call fzero with the statement:
rO = fzero('funr' ,5).
Note the single quotes around the name of the input function funr.
Use function handle: A function handle is a convenient function identifier (a
variable) created by the user. It is created with the ill symbol. We can use
it for any function-built-in or a user-written M-file function (but not an
inline function) . As examples, let us do the same thing with funr as we did
previously but with a function handle.
2 A function that uses another function inside its body is called a calling function. For example,
sol vexf in the example earlier is a calling function for the function det .