Matlab - The following error occurred converting from sym to double:

syms  x y a b

v=[1 x y x*y x^2 y^2 x^2*y x*y^2]

xi=[-a,0,a,a,a,0,-a,-a]

yi=[-b,-b,-b,0,b,b,b,0]

p=length(v)

V=zeros(p)

T=diag(ones(p,1))

i=1

 for   j=1:p

    x=xi(i,j)

    y=yi(i,j)

    eval(v)

    V(j,:)=eval(v)

 end

syms  x y a b

v=[1 x y x*y x^2 y^2 x^2*y x*y^2]

xi=[-a,0,a,a,a,0,-a,-a]

yi=[-b,-b,-b,0,b,b,b,0]

p=length(v)

V=sym(zeros(p))

T=diag(ones(p,1))

i=1

 for   j=1:p

     x=xi(i,j)

    y=yi(i,j)

    eval(v)

    V(j,:)=eval(v)

 end

clear all

syms  x y a b

v=[1 x y x*y x^2 y^2 x^2*y x*y^2];

xi=[-a,0,a,a,a,0,-a,-a];

yi=[-b,-b,-b,0,b,b,b,0];

p=length(v);

T=diag(ones(p,1));

i=1;

 for   j=1:p

    x=xi(i,j);

    y=yi(i,j);

    eval(v);

    V(j,:)=eval(v);

 end

 V

>> eval11

V =

[ 1, -a, -b,  a*b, a^2, b^2, -a^2*b, -a*b^2]

[ 1,  0, -b,    0,   0, b^2,      0,      0]

[ 1,  a, -b, -a*b, a^2, b^2, -a^2*b,  a*b^2]

[ 1,  a,  0,    0, a^2,   0,      0,      0]

[ 1,  a,  b,  a*b, a^2, b^2,  a^2*b,  a*b^2]

[ 1,  0,  b,    0,   0, b^2,      0,      0]

[ 1, -a,  b, -a*b, a^2, b^2,  a^2*b, -a*b^2]

[ 1, -a,  0,    0, a^2,   0,      0,      0]