matlab fcnchk 函数用法

fcnchk will not accept string expressions for FUN in a future release. Use anonymous functions for FUN instead.
fcnchk函数将会在以后的版本中删除，以后用匿名函数代替

fcnchk(FUN,...) returns an inline object based on FUN if FUN
is a string containing parentheses, variables, and math
operators.  fcnchk simply returns FUN if FUN is a function handle, 
or a MATLAB object with an feval method (such as an inline object). 
If FUN is a string name of a function (e.g. 'sin'), fcnchk returns a
function handle to that function.

fcnchk is a helper function for FMINBND, FMINSEARCH, FZERO, etc. so they
can compute with string expressions in addition to functions.

fcnchk(FUN,...,'vectorized') processes the string (e.g., replacing
'*' with '.*') to produce a vectorized function.

When FUN contains an expression then fcnchk(FUN,...) is the same as
INLINE(FUN,...) except that the optional trailing argument 'vectorized'
can be used to produce a vectorized function.

[F,ERR] = fcnchk(...) returns a struct array ERR. This struct is empty
if F was constructed successfully. ERR can be used with ERROR to throw
an appropriate error message if F was not constructed successfully.

简单点来说，如果将字符串传递给fcnchk函数，函数会返回inline函数(前提是这个字符串代表的函数你以经定义了)

例如我定义了一个矩形函数：

function z = rect(x)
x= abs(x); 
z = (x<1/2)*1.0 ;
z(find(x==1/2)) = 0.5;
end

上面的函数是一维的，如果我想定义一个二维的矩形函数怎么办呢？
我可以将字符串rect(x).*rect(y)传递到fcnchk函数里，会返回一个定义好了的inline函数func，可以理解为定义好了的函数句柄，

fun = 'rect(x).*rect(y)'
func = fcnchk(fun);

调用func函数，X,Y是函数的坐标

f = feval(func,X,Y);

如果想要指定输入参数的情况下，例如定义矩形函数的门宽，rect(x/w).*rect(y/w),
可以采用下面的形式

fun = 'rect(x/w).*rect(y/w)'
func = inline(fun,'x','y','w');

不过这个函数快要退出历史舞台了，还是去学匿名函数的用法吧
看到一个不错的参考资料，需要的朋友可以去看下：
http://pages.cs.wisc.edu/~cs310-1/modules/Programming/_More%20Advanced%20Functions/fcnchk%20Function/TopicDiscussion.html

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