Hi, I'm currently an undergraduate engineering student and am doing research for the summer writing programs to help analyze and study cell motility and cooperativity when introduced to certain growth factors. For specific growth factors there is a noticeable swarming movement amongst neighboring cells in our time lapse data while other growth factors induce distinct coordinating movement amongst groups of cells. As of right now I'm trying to write the portion of my program to calculate the angle between neighboring cells, the problem I'm having is maintaining a fixed origin and still returning the angle I desire. My data consists of x and y coordinates, thus my first instinct was to treat these points as 2D vectors and use the dot product to calculate the angle. However, in some of these paths there are very sharp turns where the angle I'd like to find is the obtuse angle of the turn. I've also thought of using the law of cosines but I'm not sure that it would render more accurate results than the dot product. As of now I'm not sure what direction to take my calculation and I was interested in hearing any other input on what type of calculation I possibly should think of using. Thanks again and please feel free to ask any questions as I will gladly provide more information or just answer any questions in general.