draw_arrow=function(p,x1,y1,x2,y2){
    p.push()
    p.strokeWeight(5)
    p.line(x1,y1,x2,y2)
    offset=5
    var angle = p.atan2(y1 - y2, x1 - x2); //gets the angle of the line
    p.translate(x2, y2); //translates to the destination vertex
    p.rotate(angle-p.HALF_PI); //rotates the arrow point
    p.triangle(-offset*0.8, offset, offset*0.8, offset, 0, -offset/2); //draws the arrow point as a triangle
    p.pop();

    // Return the center of the arrow
    return(p.createVector(x1+(x2-x1)/2,y1+(y2-y1)/2))
}