syms x y
wucha=0
X=[0,0.5,0.6,0.7,0.8,0.9,1.0]
Y=[1,1.75,1.96,2.19,2.44,2.71,3.00]
n=length(X);B=[]
A=ones(n,1)
B=X'
A=[A,B]
B=B.*B
A=[A,B]
C=linsolve(A,Y')
y=C(3)*x^2+C(2)*x+C(1)
x=-1.00:0.01:1.00
y=C(1)+C(2)*x+C(3)*x.^2
plot(x,y)
xlabel('x'); ylabel('y')
for i=1:n  
    x=X(i);   
    y=C(1)+C(2)*x+C(3)*x^2 
    subs(y,'x',X(i))
    wucha=wucha+(y-Y(i))^2
end
wucha 
x=-1.00:0.01:1.00
y=C(1)+C(2)*x+C(3)*x.^2;
plot(x,y);
xlabel('x'); ylabel('y');

运行后显示

?? Error using ==> plot
Conversion to double from sym is not possible.

Error in ==> C:\MATLAB6p5\work\Untitled.m
On line 24  ==> plot(x,y)

到底是什么问题，纠结一下午，我都交不了作业了，请大家帮忙