Matlab angle between two points [duplicate]

I am looking for an algorithm to calculate the angle between two points (defined by x and y valaue) in an image. The angle should be between the horizontal-line of one of these points and the line that connects the two points.

How can I do that?

How do you find the angle between two points in Matlab?

angle = atan2d(x1*y2-y1*2,x1*x2+y1*y2);

How do you find the angle between two vector points?

Formula for angle between two Vectors The cosine of the angle between two vectors is equal to the sum of the product of the individual constituents of the two vectors, divided by the product of the magnitude of the two vectors. =| A | | B | cosθ.

For points (x1,y1) and (x2,y2) use this:

atan2(y2-y1,x2-x1)

This will return the angle between a horizontal vector from (x1,y1) to (x1+1,y1) and the vector from (x1,y1) to (x2,y2).