MATLAB: Finding intersect between 2 lines.

Question

I'm trying to find out the value of x when y = 22948. I've tried the intersect and find command but can't get it to work.

clear vars

clear

clc

% Experimental Data

cpm = [45896,36896,32296,27696,20896,16396,11896,8396];

thickness = [0,1.6,2.4,3.3,4.9,6.4,9.5,12.7];

half_cpm = 22948;

% Plot data

figure()

t=plot(thickness,cpm)

hold on % Retain current figure

yline(half_cpm) % Add horizontal line at I = I0/2

xlabel('Thickness of lead (mm)');

ylabel('Background Corrected Counts per Minute (cpm)');

title('Effectiveness of lead at attenuating gamma radiation.');

Answer 1

Add this:

thick_half_cpm = interp1(cpm, thickness, half_cpm);

to get the intersection, so the full code becomes:

% Experimental Data
cpm = [45896,36896,32296,27696,20896,16396,11896,8396];
thickness = [0,1.6,2.4,3.3,4.9,6.4,9.5,12.7];
half_cpm = 22948;
thick_half_cpm = interp1(cpm, thickness, half_cpm);
% Plot data
figure()
t=plot(thickness,cpm);
hold on % Retain current figure
yline(half_cpm) % Add horizontal line at I = I0/2
plot(thick_half_cpm, half_cpm, 'pg', 'MarkerSize',15)
hold off
xlabel('Thickness of lead (mm)');
ylabel('Background Corrected Counts per Minute (cpm)');
title('Effectiveness of lead at attenuating gamma radiation.');

The intersection is plotted with a green pentagram.