vpa error in matlab

I have an important problem in writing a program for calculating Lagrange. i want to assume z as parameter. then I face this error:

""Error in MuPAD command: DOUBLE cannot convert the input expression into a double array. If the input expression contains a symbolic variable, use the VPA function instead.""

this is my program:

clear
clc
syms z
x=[0 300 1000 1500 1700 2000 3000 3300 4000 4500 5000]
y=[32.0 122.4 296.4 405.7 447.6 608.4 704.7 761.4 891.9 983 1072.6]
m=z-x
i=1
j=1
L=[1 1 1 1 1 1 1 1 1 1 1]
q=[1 1 1 1 1 1 1 1 1 1 1]
while j<12
  if j==1
      for i=2:11
           L(1)=L(1)-m(i)
          q(1)=q(1)*(x(j)-x(i))
      end
  else
            for i=1:(j-1)
            L(j)=L(j).*m(i)
            q(j)=q(j).*(x(j)-x(i))
            end
          for i=(j+1):11
          L(j)=L(j).*m(i)
          q(j)=q(j).*(x(j)-x(i))
          end
    end    
j=j+1
end
e=(y.*L)
o=e./q
k=1
f=0
while k<12
 f=f+o(k) 
 k=k+1
end
ezplot(f)