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 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 as inputs to the named function. For example,
feval ("acos", -1) ⇒ 3.1416
calls the function
acos with the argument ‘-1’.
feval can also be used with function handles of
any sort (see Function Handles). Historically,
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 whether f is a function handle,
function name in a string, or inline function then
feval can be used
A similar function
run exists for calling user script files, that
are not necessarily on the user path
Run script in the current workspace.
Scripts which reside in directories specified in Octave’s load
path, and which end with the extension ".m", can be run simply by
typing their name. For scripts not located on the load path, use
The file name script can be a bare, fully qualified, or relative filename and with or without a file extension. If no extension is specified, Octave will first search for a script with the ".m" extension before falling back to the script name without an extension.
Implementation Note: If script includes a path component, then
run first changes the directory to the directory where script
run then executes the script, and returns to the original
See also: path, addpath, source.