Ошибка Unrecognized function or variable 'x'

P=[11500,9500,9000,8500,8000,7500];
V=[100,300,400,500,600, 700];
x=V;
y=P;
Untitled;
P=f;
P1=[800,100,0,-100,-300,-400];
y=P1;
Untitled;
P1=f;
plot(V,P,V1,P1);
 
 
H=[500,1000,2000,3000,4000,5000,6000,7000];
Ro=[1.1673,1.1117,1.0066,0.9093,0.8193,0.7364,0.6601,0.5900];
x=Ro;
y=H;
Untitled;
H=f;
plot(H,Ro);
 
 
Cy=[0,0.25,0.5,0.75,1.0,1.25,1.4];
al=[2,4,7,10,13,17,20];
x=al;
y=Cy;
Untitled;
Cy=f;
plot(al,Cy);
 
 
Cx=[0.02,0.03,0.04,0.05,0.075,0.12,0.17];
al=[2,4,7,10,13,17,20];
x=al;
y=Cx;
Untitled;
Cx=f;
plot(al,Cx);

x1=sum(x);
x2=sum(x.^2);
x3=sum(x.^3);
x4=sum(x.^4);
y1=sum(y);
x1y=sum(x.*y);
x2y=sum((x.^2).*y);
k=length(x);
syms a0 a1 a2;
[a0,a1,a2]=solve(a0*x4+a1*x3+a2*x2==x2y,a0*x3+a1*x2+a2*x1==x1y,a0*x2+a1*x1+a2*k==y1,[a0,a1,a2]);
a=[a0,a1,a2];
syms f;
f=(x.^2)*a0+x.*a1+a2;

function f = Isaljack(x, y)
x1=sum(x);
x2=sum(x.^2);
x3=sum(x.^3);
x4=sum(x.^4);
y1=sum(y);
x1y=sum(x.*y);
x2y=sum((x.^2).*y);
k=length(x);
syms a0 a1 a2;
[a0,a1,a2]=solve(a0*x4+a1*x3+a2*x2==x2y,a0*x3+a1*x2+a2*x1==x1y,a0*x2+a1*x1+a2*k==y1,[a0,a1,a2]);
a=[a0,a1,a2];
syms f;
f=(x.^2)*a0+x.*a1+a2;
end

f = Isaljack(x, y);