求助：简单的函数eval函数

ylhit

我的程序是：<BR>%画自定义函数<BR>syms x y;<BR>y=input('entre your function:y=')<BR>a=0:0.1:2*pi;<BR>b=a;<BR>for i=1:length(a)<BR>    b(i)=eval(y(a(i)));<BR>end<BR>plot(x,y)<BR>  出错提示：??? Index into matrix is negative or zero.  See release notes on changes to <BR>logical indices.

happy

Eval： Execute a string containing a MATLAB expression<BR>看清楚eval是干嘛的