Question

Project 2: (Data fitting-interpolating) Write a code that uses Matlab to read the data form an excel file and try to fit the data to a polynomial of degree n, and then. Write down the analytical function that represent the data. Calculate the rms-error between the actual data and the fitted data. Plot the original data and the fitted data in one figure using the proper title and legends

Answer 1

Here is the Matlab code for the above problem:(make sure you have curve fitting tool box installed in matlab)

%% dataFitting.m
% put data in excel sheet in sheet1 in below format:
% xtitle    ytitle
% x1         y1
% x2         y2
% x3         y3
% x4         y4

clc;
[FileName,PathName] = uigetfile({'*.xlsx';'*.xls'},'Select the excel file');
[num,text,raw] = xlsread(FileName,1);
x=num(:,1);
y=num(:,2);
answer=inputdlg('Enter the degree of polynomial(degree<=9)');
answr=str2double(answer{1});
if ~isnumeric(answr)
    error('Enter a number less than or equal to 9');
    return;
end
if (answr)>9
    disp('degree can''t be greater than 9...');
    disp('proceding with degree 9 ');
    deg=9;
else
    deg=answr;
end
%% curve fitting

disp('Analytical function that represents data is:');
curve=fit(x,y,['poly' num2str(deg)])

%% plotting data

plot(curve,x,y)
title('Actual Data Vs Fitted Data');

xlabel(text(1));
ylabel(text(2));
p=coeffvalues(curve);

%% calculating rms error
yfit=polyval(p,x);
numerator = sum((yfit-y).^2);
denominator= length(x);
if length(x)==1
    denominator=1;
end
RMSError = numerator / denominator;
fprintf('RMS error between actual data and fitted data is:%f\n',RMSError);
disp('**end**');