/*
parabola: (x0,y0,x1,y1) -> (theta,v0)

Computes launch speed of the projectile (v0) with randomly given elevation
angle (theta), for known the launcher coordinate (x0,y0) and the target
coordinate (x1,y1); in case of no forces applied but the constant gravity.
*/
x0=argument0
y1=argument1
x1=argument2
y0=argument3
g=XXX //Replace with a reasonable value
theta=pi/2-random(pi/2-arctan((y1-y0)/(x1-x0)))
v0=(x1-x0)/cos(theta)*sqrt(.5*g/((x1-x0)*tan(theta)-(y1-y0)))

/*
parabola2: (x0,y0,x1,y1,ax,ay) -> (theta,v0)

Computes launch speed of the projectile (v0) with randomly given elevation
angle (theta), for known the launcher coordinate (x0,y0), the target
coordinate (x1,y1), and x-component and y-component of wind acceleration;
in case of no another forces applied.
*/
x0=argument0
y1=argument1
x1=argument2
y0=argument3
ax=argument4
ay=argument5
g=XXX //Replace with a reasonable value
do{
    theta=random(pi/2)
    k=((y1-y0)/(x1-x0)-(ay-g)/ax)/(sin(theta)-(ay-g)/ax*cos(theta))
}until(ax*(x1-x0)/(1-k*cos(theta))>=0)
v0=k*sqrt(.5*ax*(x1-x0)/(1-k*cos(theta)))