MATLAB Function Reference

feval

函式運算求值(Function evaluation)

Syntax

[y1,y2,...] = feval(fhandle,x1,...,xn)
[y1,y2,...] = feval(function,x1,...,xn)

Description

[y1,y2,...] = feval(fhandle,x1,...,xn) 使用引數 x1 到 xn來運算函式處理(function handle) fhandle。若函式處理( function handle)超過1個內建函式( built-in)或M檔案（表示這是一組包含過多函式的集合）， 則 x1 到 xn 的資料型態決定了哪個函式要先處理。(determines which function is dispatched to)

[y1,y2...] = feval(function,x1,...,xn) 若 function 為以引號來包住某個函式名稱的字串（通常定義在M檔案中），則 feval(function,x1,...,xn) 以所給定的函式和其引數來做運算。而 function 一定是單一函式的名稱，也不能包含路徑。

Note    The preferred means of evaluating a function by reference is to use a function handle. To support backward compatibility, feval also accepts a function name string as a first argument. However, function handles offer the additional performance, reliability, and source file control benefits listed in the section An Overview of Function Handles.

Remarks

下列二行命令產生一樣的結果。

[V,D] = eig(A)
[V,D] = feval(@eig,A)

Examples

下列的範例在呼叫 fminbnd.時傳一個函式處理(function handle)fhandle。 而 fhandle 是對 humps 函式的處理。( is a handle to the humps function.)

fhandle = @humps;
x = fminbnd(fhandle, 0.3, 1);

 fminbnd 使用 feval 來運算所傳入的函式處理。( evaluate the function handle that was passed in.)

function [xf,fval,exitflag,output] = ...
    fminbnd(funfcn,ax,bx,options,varargin)
            .
            .
            .
fx = feval(funfcn,x,varargin{:});

下列範例中， @deblank 回傳函式處理(function handle)給 fhandle. Examining the handle using functions(fhandle) reveals that it is bound to two M-files that implement the deblank function. The default, strfun\ deblank.m, handles most argument types. However, the function is overloaded by a second M-file (in the @cell subdirectory) to handle cell array arguments as well.

fhandle = @deblank;

ff = functions(fhandle);
ff.default
ans = 
    matlabroot\toolbox\matlab\strfun\deblank.m
ff.methods
ans = 
    cell: 'matlabroot\toolbox\matlab\strfun\@cell\deblank.m'

當函式處理運算到細胞陣列(cell array)時， feval 從引數的型態中決定適當的函式來執行，而此函式是放在 strfun\@cell中。

feval(fhandle, {'string   ','with  ','blanks        '})
ans = 
    'string'    'with'    'blanks'

See Also

assignin, function_handle, functions, builtin, eval, evalin

ferror

fft