How to find an intersection between two lines on a plot?

I have this code,

for P = [0; 1000; 2000; 6000; 10000; 12000; 12900; 13400; 13600; 13800; 14000; 14400; 15200; 16800; 18400; 20000; 22400];

Elon = [0; 0.0002; 0.0006; 0.0019; 0.0033; 0.0039; 0.0043; 0.0047; 0.0054; 0.0063; 0.0090; 0.0102; 0.0130; 0.0230; 0.0336; 0.0507; 0.1108];

d = 0.505;

r = d/2;

Area = pi*r^2;

GL = 2;

Stress = P/Area

Strain = Elon/GL

plot(Strain,Stress,'-x')

axis([0 0.06 0 120000]);

grid;

grid minor;

title('Stress vs. Strain')

xlabel('Strain')

ylabel('Stress, psi')

hold on;

text(0.00195,5.991e+04,'\leftarrow Proportional limit');

Proprtinal_limit = Stress(6)

E = (Stress(6)-Stress(1))./(Strain(6)-Strain(1))

refline(E,-30724)

axis([0 0.06 0 120000]);

end

I need to find the X and Y coordinates for the intersection of "Plot" and "refline".

[Walter Roberson]

https://www.mathworks.com/matlabcentral/fileexchange/11837-fast-and-robust-curve-intersections and similar in the File Exchange.

[darova]

Or use polyxpoly() if you have a toolbox

Answer 1

[Star Strider]

Try this:

RL = Strain*E -30724;                               % ‘refline’ As Funciton Of ‘Strain’ 
D = RL - Stress;                                    % Difference
[Du,ix] = unique(D, 'stable');                      % Unique ‘D’ & Indices

IntsctX = interp1(D(ix), Strain(ix), 0)             % Value Of ‘Strain’ At Intersection
IntsctY = E*IntsctX - 30724                         % Value Of ‘Stress’ At Intersection

producing:

IntsctX =
       0.00324479065349119

IntsctY =
          68968.0850755092