MATLAB: How to find slope for certain area in graph.

graphslope

I have this graph and i need to find the slope where is (2 – 14)
clear all;clc;
gogn = xlsread(fullfile('C:\Users\ebben\Dropbox\HR\Eðlisfræði\Verklegt\Top','TOP_gogn.xlsx'));
force=gogn(:,1);
angle=gogn(:,2);    % Data imported
                    % finding the slope
lm=fitlm(angle,force,'poly1');      
hallatala=lm.Coefficients.Estimate; 
                    % value for slope in textbox
annotation('textbox', [.3 .245 .1 .1], 'String', ...
                    ['Hallatala: ',num2str(hallatala(2,1))]);
                    % ploting data
plot(angle,force,'r.')
hold on 
                    % ploting the slope line
besta_lina=hallatala(2,1)*angle + hallatala(1,1);
plot(angle,besta_lina,'k','Linewidth',2)
xlabel('angle[rad]');
ylabel('force[N]');
grid
title(['TOP'])

Best Answer

To limit ‘angle’ (and ‘force’) to calculate the slope only on the ‘angle’ limits between 2 and 14, try this: 
Lv = (angle >= 2) & (angle <= 14);                              % Logical Vector Selecting Desired Subset
angle = angle(Lv);                                              % Limit ‘angle’
force = force(Lv);                                              % Limit ‘force’
inserting these assignments just after you initially define them.
I am not certain if you want to limit your entire analysis to those limits, or just plot that line and return the slope value in that region. Both of those are relatively straightforward to do.
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