下面是个MATLAB程序，请问fun,和feval,是什么，如何写fun,如何代表这个函数

>> help feval

FEVAL Execute the specified function.

FEVAL(F,x1,...,xn) evaluates the function specified by a function

handle or function name, F, at the given arguments, x1,...,xn.

For example, if F = @foo, FEVAL(F,9.64) is the same as foo(9.64).

If a function handle is bound to more than one built-in or

M-file, (that is, it represents a set of overloaded functions),

then the data type of the arguments x1 through xn, determines

which function is executed.

FEVAL is usually used inside functions which take function

handles or function strings as arguments. Examples include

FZERO and EZPLOT.

[y1,..,yn] = FEVAL(F,x1,...,xn) returns multiple output arguments.

Within methods that overload built-in functions, use BUILTIN(F,...)

to execute the original built-in function. Note that when using

BUILTIN, F must be a function name and not a function handle.

See also assignin, function_handle, functions, builtin, eval, evalin.

Overloaded methods:

inline/feval

sfit/feval

fittype/feval

cfit/feval

evalExpr/feval

mbcinline/feval

Reference page in Help browser

doc feval

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fun就是自己写的函数了

&这个是引用的意思。

第一次fun（x,y），即fun（x=5，y=10），x+=y,x=5+10=15 y+x=x, y=y+x ,y=10+15=25

因为y是引用的，即 main函数里的y=25.

同理第二次 x 被引用 fun（x=10，y=25） ,x+=y ,x=10+25=35

所以mian中x = 35

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