boids

I'm trying to program the behaviour of birds in flight with boids in Python. I haven't found much yet but currently i'm stuck on the function defining the distance between two boids. It has to be calculated with the formula (a,b) = sqrt( (a_x - b_x)^2 + (a_y - b_y)^2) ) where a and b are the two vectors between which i have to calcualte the distance, a_x and b_x are the x-components of the vectors and a_y and b_y are the y-components. I get an error about the indices in the formula. I've tried solving in in a number of ways but i just can't figure out how to do it... Here is what i've got so

Yesterday I came across Craig Reynolds' Boids , and subsequently figured that I'd give implementing a simple 2D version in Java a go. I've put together a fairly basic setup based closely on Conrad Parker's notes . However, I'm getting some rather bizarre (in my opinion) behaviour. Currently, my boids move reasonably quickly into a rough grid or lattice, and proceed to twitch on the spot. By that I mean they move around a little and rotate very frequently. Currently, I have implemented: Alignment Cohesion Separation Velocity limiting Initially, my boids are randomly distributed across the