Many students ask me how do I do this or that in MATLAB. So I thought why not have a small series of my next few blogs do that. In this blog, I show you how to conduct spline interpolation.

- The MATLAB program link is here.
- The HTML version of the MATLAB program is here.
- DO NOT COPY AND PASTE THE PROGRAM BELOW BECAUSE THE SINGLE QUOTES DO NOT TRANSLATE TO THE CORRECT SINGLE QUOTES IN MATLAB EDITOR. DOWNLOAD THE MATLAB PROGRAM INSTEAD

%% HOW DO I DO THAT IN MATLAB SERIES?

% In this series, I am answering questions that students have asked

% me about MATLAB. Most of the questions relate to a mathematical

% procedure.

%% TOPIC

% How do I do spline interpolation?

%% SUMMARY

% Language : Matlab 2008a;

% Authors : Autar Kaw;

% Mfile available at

% http://numericalmethods.eng.usf.edu/blog/interpolate_spline.m;

% Last Revised : June 20, 2009;

% Abstract: This program shows you how to do spline interpolation?

% .

clc

clear all

clf

%% INTRODUCTION

disp(‘ABSTRACT’)

disp(‘ This program shows you how to do spline interpolation?’)

disp(‘ ‘)

disp(‘AUTHOR’)

disp(‘ Autar K Kaw of https://autarkaw.wordpress.com’)

disp(‘ ‘)

disp(‘MFILE SOURCE’)

disp(‘ http://numericalmethods.eng.usf.edu/blog/interpolation_spline.m’)

disp(‘ ‘)

disp(‘LAST REVISED’)

disp(‘ June 20, 2009’)

disp(‘ ‘)

%% INPUTS

% y vs x data to interpolate

% x data

x=[-1 -0.75 -0.5 -0.25 0.25 0.50 0.75 1];

% ydata

y=[-0.5 -0.5 -0.5 -0.5 0.5 0.5 0.5 0.5];

% Where do you want to interpolate at

xin=[-0.8 -0.7 0.7 0.8];

%% DISPLAYING INPUTS

disp(‘INPUTS’)

disp(‘The x data’)

x

disp(‘The y data’)

y

disp(‘The x values where you want to find the interpolated values’)

xin

disp(‘ ‘)

%% THE CODE

% Fitting to spline – it is cubic splines

yin=spline(x,y,xin);

% This is only for plotting the spline interpolants

% Find the number of data points

n=length(x);

xplot=x(1):(x(n)-x(1))/10000:x(n);

yplot=spline(x,y,xplot);

%% DISPLAYING OUTPUTS

disp(‘ ‘)

disp(‘OUTPUTS’)

disp(‘x values at which function is to be interpolated’)

xin

disp(‘y values at the xin values’)

yin

xlabel(‘x’);

ylabel(‘y’);

title(‘y vs x ‘);

plot(x,y,’o’,’MarkerSize’,10,’MarkerEdgeColor’,’b’,’MarkerFaceColor’,’b’)

hold on

plot(xin,yin,’o’,’MarkerSize’,10,’MarkerEdgeColor’,’r’,’MarkerFaceColor’,’r’)

hold on

plot(xplot,yplot,’LineWidth’,2)

legend(‘Points given’,’Points found’,’Spline Curve’,’Location’,’East’)

hold off

disp(‘ ‘)

This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu, the textbook on Numerical Methods with Applications available from the lulu storefront, and the YouTube video lectures available at http://numericalmethods.eng.usf.edu/videos and http://www.youtube.com/numericalmethodsguy

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