How can we Plot a line passing through two points?

I am given two points (x1,y1) and (x2,y2). How can I plot a line that will pass through these two points and extend till the x and y axis?

Answer 1

[David Sanchez]

If you want a line connecting A and B:

A = [2 3]; 
B = [4 5]; 
plot(A,B,'*')
axis([0 10 0 10])
hold on
line(A,B)
hold off

If you want a line through A and B that extend to the plt limits:

xlim = get(gca,'XLim');

m = (B(2)-B(1))/(A(2)-A(1));
n = B(2)*m - A(2);

y1 = m*xlim(1) + n;
y2 = m*xlim(2) + n;
hold on
line([xlim(1) xlim(2)],[y1 y2])
hold off

[Emmanuel]

Hey!! Thanks a lot! Now my lines are intersecting when I changed the xlim from [-10 10] from your code. But the form a triangle in the negative axis

[Tunhe Zhou]

n = B(2)*m - A(2); This seems to be n = B(2) - A(2)*m;

[Goku]

Thank you. But How can this be done in 3D ?

[nobody]

above meaning connecting the two points P1=[A(1),B(1)] and P2=[A(2),B(2)]

If you want to connect the two points C=[2,3] and D=[4,5] you do

m = (D(2)-C(2)) / (D(1)-C(1)); %slope

n = C(2) - C(1)*m %vertical shift from [0,0]

y1 = m*xlim(1) + n;

y2 = m*xlim(2) + n;

don't you?

[Ronaldo Lim]

excuse me, why do you use "vertival shift from [0,0]" . What's that ?

Answer 2

[Mahesh]

A = (x1,y1); B = (x2,y2);

plot(A,B)

[Mahesh]

Example: Want to draw the line b/w the points (5,10) and (15,30).

A = (5,15); B = (10,30); plot(A,B)

[Emmanuel]

monospaced Thanks!!

[Adam Danz]

No, this is incorrect. With the syntax plot(A,B), A contains x-values and B contains y-values. Instead, Mahesh defined A and B as (x,y) coordinates.

A simple test will show that this is incorrect,

A = [1,2];
B = [ -3,4];
plot(A,B)
hold on
plot(A(1),A(2), 'r*')
plot(B(1),B(2), 'k*')
legend('line','A','B','Location','BestOutside')
axis padded

To connect coordinates A-B you must use,

plot([A(1),B(1)], [A(2),B(2)])

[Peter Hansen]

First of all, you need to understand that mathlab is made for matrixes and arrays, to easy big data calculation.

So all data is ussaly needed in matrix or arrays.

Therfor when ploting points, you dont plot single points like A and B but and array of x-cordinates of A and B and a array of y-cordinates of A and B.

maybe this will claryfy it for you :)

figure(2); clf(2); hold on; axis([0 10 0 10]); axis padded 

% If Point A is in x=1 and y=2 
% If Point B is in x=-3 and y=4 
% If Point C is in x=-6 and y=-4 
x_array = [1 -3 -6]; 
y_array = [2 4 -4]; 

plot(x_array(1),y_array(1),'*') % A 
plot(x_array(2),y_array(2),'*') % B 
plot(x_array(3),y_array(3),'*') % C 

% OR to plot all points at once uncoment below line insted, and remve ",'B','C'" from legend
% plot(x_array,y_array,'*') % A, B and C


line(x_array,y_array) % line 

legend('A','B','C','line','Location','BestOutside') hold off