Polyfit matrix from import TXT file

Hi, I am trying to import a TXT file containing 100 rows x 2 columns of data. I then want to take that data and polyfit it. However, what I have been trying so far receives the errror: Warning: Polynomial is not unique; degree >= number of data points. All of my matrices come out with correct data.

My current code:

% Import data
filename = 'A2Q2_input_a.txt';
delimiterIn = ' ';
headerlinesIn = 1;
A = importdata(filename);

for k = [1:100]
    D = (A.data(k, :));
    domain(k) = D(1));
    percent_err(k) = D(2);
    
    % perform linear polyfit function
    p_linear_R4 = polyfit(domain,percent_err,1);

[Rik]

You forgot to attach your file.

But the problem is deeper: you are only giving polyfit scalar values to determine a polynomial, which you overwrite every iteration. Is that what you intended to do? Because the rest of your question sounds like you want a single polynomial to be fitted to your entire matrix.

[Tate Kafka]

Yes i would like a single polynomial to be fitted to the entire matrix

[Rik]

Then the answer posted by KSSV should be what you need. If not, attach the file to your question and explain why it doesn't work.

Answer 1

[KSSV]

% Import data
filename = 'A2Q2_input_a.txt';
T = readtable(filename);
x = T.(1) ;
y = T.(2) ; 
% perform linear polyfit function
p_linear_R4 = polyfit(x,y,1);
yi = polyval(p_linear_R4,x) ;
figure
hold on
plot(x,y,'.b')
plot(x,yi,'r')