Calculating Error and intercept on a log plot

Hi there,

this is the code/ data I have. Please note I have already taken the logs so that the data is scaled appropriately.

Log_N = [1.09861228866811,1.09861228866811,1.79175946922806,2.56494935746154,3.61091791264422,4.23410650459726,4.65396035015752];
Log_R = [-2.50000000000000,-2,-1.50000000000000,-1,-0.500000000000000,0,0.500000000000000];
plot(Log_R,Log_N,'o')
hold on 
title('Correlation Dimension')
xlabel('Log R')
ylabel('Log Nd')
hold on 
[P, S,] = polyfit(Log_R,Log_N,1);
 
% Evaluate the fitted polynomial p and plot:
f = polyval(P,Log_R);
plot(Log_R,Log_N,'o',Log_R,f,'-')
legend('data','linear fit')

I have created my line of best fit using polyfit and polyval. All I am wanting to do is fit a straight line to my data and would like to know my gradient of the line/ slope and the associated error.

Any advice would be much appreciated.

I tried using 'fit'

[curve, ~] = fit(Log_R, Log_N,'poly1');

but the errors I got were:

>> correlation_attempt_2
Error using fit>iFit (line 127)
X must be a matrix with one or two columns.

Error in fit (line 108)
[fitobj, goodness, output, convmsg] = iFit( xdatain, ydatain, fittypeobj, ...

Error in correlation_attempt_2 (line 72)
[curve, ~] = fit(Log_R, Log_N,'poly1');

Answer 1

[KALYAN ACHARJYA]

ERROR

Error using fit>iFit (line 127)
X must be a matrix with one or two columns.
Error in fit (line 108)
[fitobj, goodness, output, convmsg] = iFit( xdatain, ydatain, fittypeobj, ...
Error in ans_matlab_april19 (line 17)

Threfore I did transpose

[curve, ~]=fit(Log_R', Log_N','poly1');
figure, plot(curve,Log_R,Log_N)

[P_L]

Many Many thanks!! solved my problem!

I am trying to amend my data points so that appear larger- the 'MarkerSize' command isn't working - is there another way I need to do it?

This is what I am trying:

figure, plot(curve,Log_R,Log_N,'o','MarkerSize',12, 'MarkerFaceColor', 'b')