>> xs = linspace(0,pi,5);
>> ys = sin(xs);
>> plot(xs,ys,'o','LineWidth',2)
>> pp=spline(xs,ys);
>> pp

pp = 

  struct with fields:

      form: 'pp'
    breaks: [0 0.7854 1.5708 2.3562 3.1416]
     coefs: [4×4 double]
    pieces: 4
     order: 4
       dim: 1

>> ppval(pp,0)

ans =

     0

>> ppval(pp,pi/2)

ans =

     1

>> x=linspace(0,pi,100);
>> plot(x,sin(x),xs,ys,'o','LineWidth',2);
>> plot(x,sin(x),xs,ys,'o',x,ppval(pp,x),'LineWidth',2);

>> plot(x,sin(x)-ppval(pp,x),'LineWidth',2);