查看doc feval：
[y1, y2, ...] = feval(fhandle, x1, ..., xn)
[y1, y2, ...] = feval(fname, x1, ..., xn)
[y1, y2, ...] = feval(fhandle, x1, ..., xn) evaluates the function handle, fhandle, using arguments x1 through xn. If the function handle is bound to more than one built-in or .m function, (that is, it represents a set of overloaded functions), then the data type of the arguments x1 through xn determines which function is dispatched to.
[y1, y2, ...] = feval(fname, x1, ..., xn). If fname is a quoted string containing the name of a function (usually defined within file having a .m file extension), then feval(fname, x1, ..., xn) evaluates that function at the given arguments. The fname parameter must be a simple function name; it cannot contain path information.
意思很清楚，feveal就是把已知数据和符号带入已定义好的函数或函数句柄中，简单理解就是求函数的值用的。
例如:
假设需要调用的函数foo定义如下：
function x=foo(a,b)
x=a*b;
若在main函数中用feval调用foo，可以有以下几种方式
1. result=feval(‘foo‘,3,15);
2. result=feval(@foo,3,16); %这里@foo即句柄
等价于result = x(3,15)。
详细参见： http://www.cnblogs.com/begtostudy/archive/2012/06/27/2565920.html