feval function allows you to call a function from a string
containing its name. This is useful when writing a function that needs to
call user-supplied functions. The
feval function takes the name
of the function to call as its first argument, and the remaining
arguments are given to the function.
The following example is a simple-minded function using
that finds the root of a user-supplied function of one variable using
function result = newtroot (fname, x) # usage: newtroot (fname, x) # # fname : a string naming a function f(x). # x : initial guess delta = tol = sqrt (eps); maxit = 200; fx = feval (fname, x); for i = 1:maxit if (abs (fx) < tol) result = x; return; else fx_new = feval (fname, x + delta); deriv = (fx_new - fx) / delta; x = x - fx / deriv; fx = fx_new; endif endfor result = x; endfunction
Note that this is only meant to be an example of calling user-supplied
functions and should not be taken too seriously. In addition to using a
more robust algorithm, any serious code would check the number and type
of all the arguments, ensure that the supplied function really was a
function, etc. See Predicates for Numeric Objects, for example,
for a list of predicates for numeric objects, and see Status of Variables, for a description of the
Evaluate the function named name. Any arguments after the first are passed on to the named function. For example,feval ("acos", -1) ⇒ 3.1416
calls the function
acoswith the argument ‘-1’.
fevalcan also be used with function handles of any sort (see Function Handles). Historically,
fevalwas the only way to call user-supplied functions in strings, but function handles are now preferred due to the cleaner syntax they offer. For example,f = @exp; feval (f, 1) ⇒ 2.7183 f (1) ⇒ 2.7183
are equivalent ways to call the function referred to by f. If it cannot be predicted beforehand that f is a function handle or the function name in a string,
fevalcan be used instead.
A similar function
run exists for calling user script files, that
are not necessarily on the user path
Run scripts in the current workspace that are not necessarily on the path. If script is the script to run, including its path, then
runchanges the directory to the directory where script is found.
runthen executes the script, and returns to the original directory.
See also: system.