x=[385,560,621,655,676,695,711,728,750,776,806,837,858,880,900,923,943,982,1040,1120,1352]; 
y=[0.3,0.7,1,1.2,1.35,1.5,1.65,1.8,2,2.15,2.22,2.10,1.95,1.8,1.65,1.5,1.35,1.2,1,0.8,0.5]; 
knots = 10; K = 4; 
sp1 = spap2(knots,K,x,y); 

plot(x,y,'ok');
hold on;
fnplt(sp1,'b') ;