How can we Plot a line passing through two points?

Question

Emmanuel 2014-5-29

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https://ww2.mathworks.cn/matlabcentral/answers/131603-how-can-we-plot-a-line-passing-through-two-points

评论： Peter Hansen 2021-8-17

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?

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Answer 1

David Sanchez 2014-5-29

3
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/131603-how-can-we-plot-a-line-passing-through-two-points#answer_138718

在 MATLAB Online 中打开

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

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nobody 2020-9-11

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 2020-11-27

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

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Answer 2

Mahesh 2014-5-29

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/131603-how-can-we-plot-a-line-passing-through-two-points#answer_138715

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

plot(A,B)

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Adam Danz 2021-6-4

编辑：Adam Danz 2021-6-4

在 MATLAB Online 中打开

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 2021-8-17

在 MATLAB Online 中打开

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