piecewise polynomials - ppval . I dont understand it

How works ppval ?

If I try to program it with 4 single polynomes in a for-loop with breaks I get a different result compare to ppval.

[breaks,coefs,l,k,d] = unmkpp(pp1);

breaks = [ -1 -0.02 0 0.02 1 ]

coefs =

   -0.0122    0.0092    0.1976
 -513.7771   -0.0146    0.1950
  496.5038  -20.5657   -0.0108
    0.0045   -0.7056   -0.2235

p1= coefs(1,1:3); % first polynom coefs

p2= coefs(2,1:3); % second polynom coefs

p3= coefs(3,1:3); % third polynom coefs

p4= coefs(4,1:3); % fourth polynom coefs

x= linspace(-1,1,1000)';

for n=1:1ooo

    if x(n)<=breaks(2)
        y1(n)=p1(3)+p1(2)*x(n)+p1(1)*x(n).*x(n);
    else
        y1(n)=0;
    end

    if x(n)>breaks(2) & x(n)<=breaks(3)
        y2(n)=p2(3)+p2(2)*x(n)+p2(1)*x(n).*x(n);
    else
        y2(n)=0;
    end

    if x(n)>breaks(3) & x(n)<=breaks(4)
        y3(n)=p3(3)+p3(2)*x(n)+p3(1)*x(n).*x(n);
    else
        y3(n)=0;
    end

    if x(n)>breaks(4)
        y4(n)=p4(3)+p4(2)*x(n)+p4(1)*x(n).*x(n);
    else
        y4(n)=0;
    end

    y(n)=y1(n)+y2(n)+y3(n)+y4(n);

end;