PolyinterpDemo.m

Contents

Overview

Illustrates polynomial interpolation by calling polyinterp from NCM (which evaluates the polynomial interpolating the data in the vectors x and y at the list of points in the vector u)

As output we get plots of

Initialization

clear all
close all
% Define the data and evaluation points
x = [2 2.5 4];
y = [0.5 0.4 0.25];
u = linspace(1,5,20)

u =

  Columns 1 through 10

    1.0000    1.2105    1.4211    1.6316    1.8421    2.0526    2.2632    2.4737    2.6842    2.8947

  Columns 11 through 20

    3.1053    3.3158    3.5263    3.7368    3.9474    4.1579    4.3684    4.5789    4.7895    5.0000

Call polyinterp

Evaluate quadratic polynomial interpolant at all the points in u

v = polyinterp(x,y,u);

Plots

Plot the data

hold on
xlim([1 5])
ylim([0 1])
plot(x,y,'bo','LineWidth',2)
legend('Data')
pause

Plot the values computed with polyinterp

plot(u,v,'g*','LineWidth',2)
legend('Data','Values from polyinterp')
pause

Let MATLAB do some more interpolation to get a continuous graph

plot(u,v,'r','LineWidth',2)
legend('Data','Values from polyinterp','MATLAB graph')
hold off

Published with MATLAB® 7.9