How can i find the minimum value of spline data

How can i find the minimum value of spline curve.

My code is below:

x=[0 0.34906585 0.698131701 1.047197551 1.396263402 1.745329252 2.094395102 2.443460953 2.792526803]
y=[0  0.342020143  0.64278761  0.866025404  0.984807753  0.984807753  0.866025404  0.64278761  0.342020143]
s=spline(x,y)
min(ppval(s))

it does not work

Answer 1

[Alan Stevens]

Change your last two lines to:

s=spline(x,y);
min(ppval(s,x))

(though it's fairly clear that the minimum occurs at x = 0!)

[esat gulhan]

Hi, thanks anywa but when i try min another spline data

x=[0 0.592699082 1.185398163 1.878097245 2.570796327 3.263495408 3.95619449 4.648893572 5.341592654]
y=[0  -0.55860177  -0.926648825  -0.953153478  -0.540302306  0.121601061  0.727452453  0.997984844  0.808496404]
s=spline(x,y);
min(ppval(s,x))

the answer is -0.953153478, it is wrong, it is the minimum of vector y not the minimum of spline (x,y)

The real minimum of this spline is at aproximately -0.99942679143809 at 1.5707963 it is smaller then -0.95.

So how can i find the real miniumum of spline

[Alan Stevens]

You need a much finer resolution for the interpolation. Try

x=[0 0.592699082 1.185398163 1.878097245 2.570796327 3.263495408 3.95619449 4.648893572 5.341592654];
y=[0  -0.55860177  -0.926648825  -0.953153478  -0.540302306  0.121601061  0.727452453  0.997984844  0.808496404];
X = 0:0.01:max(x);
Y=spline(x,y,X);
plot(X,Y)
min(Y)