Howto make all points start from [0,0] and goto [1,0] 
and make my loop not overwrite my initial conditions for the next steps?

M:=10; N:=1000;

for i to M do
X[i, 0] := 0;
Y[i, 0] := 0;
X[i, 1] := 1;
Y[i, 1] := 0;
for j to N do
Vinkel := c*rand()-Pi;
X[i, j] := X[i, j-1]+cos(Vinkel);
Y[i, j]:= Y[i, j-1]+sin(Vinkel)
end do:
end do :

1. Make a plot wich shows CD(R) as a function of R for R=1..10000. V0=abs(V), V=[vx,vy] (d,rho,mu are constants)

2. Also make a plot wich shows log10(CD(R) as a function of log10(R) in same range R=1..10000
Use y=log10(R)

I appreciate any help .

restart;
globale values, small water droplet in gravity field  , through air with velocity V=[vx,vy]  ,v=abs(V)  total dragforce kan be written FDD=abs(FD)

mu := 0.18e-4; rho := 1, 2; d := .2; Co := .4;
#abs(FD) divided into  FDx og FDy
%;

FDx := (3*Pi*mu*d+(1/8)*Pi*Co*rho*d^2*abs(v))*vx;




FDy := (3*Pi*mu*d+(1/8)*Pi*Co*rho*d^2*abs(v))*vy;

# Define v=[vx,vy] to abs(v) wich gives the length of v (scalar value)


v := proc (vx, vy) options operator, arrow; (vx^2+vy^2)^.5 end proc;

#Make FDx og FDy to  abs(FD) 

FD := sqrt(FDx^2+FDy^2);

#Define total dragforce

FDD := (1/8)*Cd*abs(v)*Pi*d^2*abs(v^2);

#Total dragforce can be writte like FDD=abs(FD), solve for Cd(v)

FD1 := solve(FD = FDD, Cd);

#Make a function which returns Cd(v) 

Cd := proc (v) options operator, arrow; 63.66197724*FD1/abs(v)^3 end proc;

HOWTO GET MY Cd(v) to return values ?????

Ive got some problem understand the use of = and := , and how to get my Cd function to mangage the v expression. A copy (in norwegian) from my assignment to see the formulas is attached. Im thankfull for any help.

inl1d.pdf

I've got a rain drop falling through air with velocity V=[vx,vy] when exposed to to dragforce Fd

formulas in following link 

Exposed_for_drag_force.docx

But  Fd= (expression for dragforce*v)* V

How to multiply V=[vx,vy] and recive list for all values so i can make a plot with this values?

need to use Cd= V ->… and returns Cd(v) (not proc..)