How to find angle between two lines?

For example, there is line L1 between two points (x1,y1) and (x2,y2). Another line L2 between points (x1,y1) and (x3,y3). I want to find the angle between the lines L1, L2. How to find in MATLAB? I think in matlab there is no predefined function which performs the same.

[James Tursa]

https://www.mathworks.com/matlabcentral/answers/101590-how-can-i-determine-the-angle-between-two-vectors-in-matlab

[sudeep]

TURE AND

Example 1: Find the angle between r1 = 2(1 + cost) and r23(1-cost) and plot the graph for the same.

Answer 1

[Bjorn Gustavsson]

A more stable method that what Jos suggested is

v_1 = [x2,y2,0] - [x1,y1,0];
v_2 = [x3,y3,0] - [x1,y1,0];
Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2));

HTH

[Beulah A]

Thanks, This solves my problem.

[jari jafri]

I got my V_1 and V_2 vectors as

v_1 =

1×3 int32 row vector

-633 990 0

v_2 =

1×3 int32 row vector

0 500 0

But i am having the following error so I 'm looking for how to remove this error

Error using norm

First argument must be single or double.

Error in test6 (line 64)

Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2));

I'm getting this error while using this code

[Dyuman Joshi]

@jari jafri convert the data to double -

v_1 = int32([-633 990 0]);
v_2 = int32([0 500 0]);

v_1 = double(v_1);
v_2 = double(v_2);

Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2))

Theta = 0.5689

Answer 2

[Jos (10584)]

Use the dot product between the two vectors (v1 and v2) given by the four x,y pairs points.

Given the formula: dot(v1,v2) = | v1 | x | v2 | x cos(A)

I leave it to you to find the angle A using the matlab functions norm, dot and acos.

More info: https://en.wikipedia.org/wiki/Dot_product

Answer 3

[Bjorn Gustavsson]

Look and you will find.

HTH