问Matlab中符号变量的替换?

EN

    function A_j = po(j,k)            % Adomian polynomials
       if j >0
         x =  sym('x',[1 j])
         syms p                       % Assinging a symbolic variable for p
         syms x0
         S = x0+ sum(p.^(1:j) .* x) ; % Sum of p*x up to order j
         Q =f(S,k);                   
         A_nc = diff(Q,p,j)/factorial(j);    
         A_j = subs(A_nc,p,0) ;            % Filling in p=0
       else
        syms x0
        S = x0; 
        A_j =f(S,k);                    
       end
    end 

    function F = f(x,k) % Nonlinear function of k power
             F = x^k ;
    end

x0 = @(t) t^{2}
K = matlabFunction(subs(po(0,2)))
x1 =integral(K,0,1)
K= matlabFunction(subs(po(1,2)))
x2 = integral(K,0,1)
K= matlabFunction(subs(po(2,2)))
x3 = integral(K,0,1)
etc