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Evaluate piecewise polynomial



v = ppval(pp,xq) evaluates the piecewise polynomial pp at the query points xq.


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Create a piecewise polynomial that has a cubic polynomial in the interval [0,4], a quadratic polynomial in the interval [4,10], and a quartic polynomial in the interval [10,15].

breaks = [0 4 10 15];
coefs = [0 1 -1 1 1; 0 0 1 -2 53; -1 6 1 4 77];
pp = mkpp(breaks,coefs)
pp = struct with fields:
      form: 'pp'
    breaks: [0 4 10 15]
     coefs: [3x5 double]
    pieces: 3
     order: 5
       dim: 1

Evaluate the piecewise polynomial at many points in the interval [0,15] and plot the results. Plot vertical dashed lines at the break points where the polynomials meet.

xq = 0:0.01:15;
line([4 4],ylim,'LineStyle','--','Color','k')
line([10 10],ylim,'LineStyle','--','Color','k')

Create and plot a piecewise polynomial with four intervals that alternate between two quadratic polynomials.

The first two subplots show a quadratic polynomial and its negation shifted to the intervals [-8,-4] and [-4,0]. The polynomial is


The third subplot shows a piecewise polynomial constructed by alternating these two quadratic pieces over four intervals. Vertical lines are added to show the points where the polynomials meet.

cc = [-1/4 1 0]; 
pp1 = mkpp([-8 -4],cc);
xx1 = -8:0.1:-4; 

pp2 = mkpp([-4 0],-cc);
xx2 = -4:0.1:0; 

pp = mkpp([-8 -4 0 4 8],[cc;-cc;cc;-cc]);
xx = -8:0.1:8;
hold on
line([-4 -4],ylim,'LineStyle','--')
line([0 0],ylim,'LineStyle','--')
line([4 4],ylim,'LineStyle','--')
hold off

Input Arguments

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Piecewise polynomial, specified as a structure. You can create pp using spline, pchip, makima, interp1, or the spline utility function mkpp.

Query points, specified as a vector or array. xq specifies the points where ppval evaluates the piecewise polynomial.

Data Types: single | double

Output Arguments

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Piecewise polynomial values at query points, returned as a vector, matrix, or array.

If pp has [d1,..,dr]-valued coefficients (nonscalar coefficient values), then:

  • When xq is a vector of length N, v has size [d1,...,dr,N], and v(:,...,:,j) is the value at xq(j).

  • When xq has size [N1,...,Ns], v has size [d1,...,dr,N1,...,Ns], and v(:,...,:, j1,...,js) is the value at xq(j1,...,js).

Extended Capabilities

Version History

Introduced before R2006a

See Also

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