求哪位高手赐教一下

求为什么程序会出错，求哪位高手赐教一下？
画正态分布的图

t=0:0.005:0.5;
>> n=length(t);
>> for i=0:n
y='1./sqrt(2*pi)*exp(-x.^2/2)';
y(i)=quadl(y,-100,0.05*i);
end
结果出错：Subscript indices must either be real positive integers or logicals.