MATLAB: Undefined function or variable ‘y’.

Question

I try to create function, but get strange error "Undefined function or variable 'y'.", i have same code but not in function and it is works, why function gave me this error?

PS Comment\Uncomment a(1,1)

syms i j x y
n = 3;
lambda = 1;
mu = 1;
x_min = 0;
x_max = 1;
y_min = 0;
y_max = 1;
p = @(x,y) x+2.*y
N = sym('N',[1 n])
for k = 1:n
    N(k) = @(x,y) sin(k.*pi.*x./n).*sin(k.*pi.*y./n);
end
i = 1
j = 1
f = @(x,y,i,j) p(x,y).* N(i).* N(j)
h = @(y) int(f(x,y,i,j), x, x_min, x_max)
vpa(int(h(y), y, y_min, y_max)) 
a(1,1)
function fun = a(j,i)
f = @(x,y,i,j) p(x,y).* N(i).* N(j)
h = @(y) int(f(x,y,i,j), x, x_min, x_max)
fun = vpa(int(h(y), y, y_min, y_max)) 
end

Answer 1

Found solution:

a(1,1,x,y,p,N,x_min,x_max,y_min,y_max)
function fun = a(j,i,x,y,p,N,x_min,x_max,y_min,y_max)
f = @(x,y,i,j) p(x,y).* N(i).* N(j);
h = @(y) int(f(x,y,i,j), x, x_min, x_max);
fun = vpa(int(h(y), y, y_min, y_max)); 
end