how to vectorize a function?

I ran the following and got some reply:

>> y=@(x)x^2;

>> fplot(y)

警告: 函数处理数组输入时行为异常。要改善性能，请将您的函数正确向量化，以返回大小和形状与输入参数相同的输出。

> In matlab.graphics.function.FunctionLine>getFunction

In matlab.graphics.function.FunctionLine/updateFunction

In matlab.graphics.function.FunctionLine/set.Function_I

In matlab.graphics.function.FunctionLine/set.Function

In matlab.graphics.function.FunctionLine

In fplot>singleFplot (line 237)

In fplot>@(f)singleFplot(cax,{f},limits,extraOpts,args) (line 192)

In fplot>vectorizeFplot (line 192)

In fplot (line 162)

>>

What is the problem?