??? Undefined function or variable 'imhistc'.是怎么回事啊。

[hfutqianwei]

我今天在一本书上面抄了一段利用MATLAB语言编写的绘制图像直方图的程序，
function [yout ,x] = imhist(varargin)
[a,n,isScaled,top,map,err_msg] = parse_inputs(varargin{:});
y = imhistc(a,n,isScaled,top);%call MEX file to do work
然后就提示
??? Undefined function or variable 'imhistc'.

Error in ==> d:\MATLAB6p5\work\Imhist.m
On line 6 ==> y = imhistc(a,n,isScaled,top); % Call MEX file to do work
不知道是什么原因？？