MATLAB Function Reference

ppval

Evaluate piecewise polynomial.

Syntax

• v = ppval(pp,xx)
  v = ppval(xx,pp)
  

Description

v = ppval(pp,xx) returns the value at the points xx of the piecewise polynomial contained in pp, as constructed by spline or the spline utility mkpp.

v = ppval(xx,pp) returns the same result but can be used with functions like fminbnd, fzero and quad that take a function as an argument.

Examples

Compare the results of integrating the function cos

• a = 0; b = 10;
  int1 = quad(@cos,a,b,[],[])
  
  int1 =
     -0.5440
  

with the results of integrating the piecewise polynomial pp that approximates the cosine function by interpolating the computed values x and y.

• x = a:b; 
  y = cos(x);
  pp = spline(x,y);
  int2 = quad(@ppval,a,b,[],[],pp)
  
  int2 =
     -0.5485
  

int1 provides the integral of the cosine function over the interval [a,b], while int2 provides the integral over the same interval of the piecewise polynomial pp.

See Also

mkpp, spline, unmkpp

pow2

prefdir