How to find an equilibrium point between two lines?

Hi guys could you help me find the equilibrium point between my demand and supply curves cheers.

This is the code I wrote, I tried using the command "solve", but I did not succeed

x = 1:20:14;
xticks(1:1:30)
y1 = -3*x +90;
plot (x,y1,'b')
hold on 
x = 1:0.5:30;
y2 = 10+x;
plot (x,y2,'c')
hold on
x = 1:0.5:30;
y3 = -3*x +60;
plot (x,y3,'b')
plot (x,y1,y2,y3)
ylim([0 100])
hold on
legend ('0G demand curve','OG supply curve','tax(30)')
title ('Market Equilibrium')
xlabel('Quantitites')
ylabel('Price')
hold off 

P = InterX([x1;y1],[x;y2]);
plot(x,y1,x,y2,P(1,:),P(2,:));

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Mark Sherstan]

You were close! The x domain must be the same length and some of your variables were mislabeled. I quickly cleaned up your code and this should work for you:

x = 1:0.5:30;

y1 = -3*x +90;
y2 = 10+x;
y3 = -3*x +60;

plot(x,y1,'b', x,y2,'c', x,y3,'b')
ylim([0 100])

title ('Market Equilibrium')
xlabel('Quantitites')
ylabel('Price')

P12 = InterX([x;y1],[x;y2])'
P23 = InterX([x;y2],[x;y3])'

hold on 
plot(P12(1,1),P12(1,2),'ro')
plot(P23(1,1),P23(1,2),'ko')
legend ('0G demand curve','OG supply curve','tax(30)','Intersection Y1-Y2', 'Intersection Y2-Y3')
hold off

[Joao Pereira]

Hi Mark I run your code but there's somekind of mistake this what I got

>> Untitled4

Unrecognized function or variable 'InterX'.

Error in Untitled4 (line 14)

P12 = InterX([x;y1],[x;y2]);

Do you have any idea of what happened?

[Image Analyst]

InterX is YOUR code, not Mark's. Evidently you never had it so why did you write in a call to InterX if you don't even know what it is? Did you write the code? If not, ask the author to give you the InterX function in an m-file, or variable in a .mat file.

[Mark Sherstan]

Adding to Image Analyst's comment make sure InterX is in the same directory as the other script. I am assuming you need to use this function: https://www.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections?focused=5165138&tab=function

[Joao Pereira]

Thank you Mark I was working with that function I’ll just keep trying

[Mark Sherstan]

As long as the function and my code is in the same folder it will work, I just tested it. So if you need more help just ask!