# Plotting a spiral in MATLAB knowing the start and end points and number of turns?

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Alec Lothian on 23 Nov 2018
Commented: km meenu on 19 Jul 2020
I found a code and was able to modify it into the following code to creaet a spiral that starts at the point I want it to but I can't seem to get it to end where I want it to and have the desired numer of turns.
t = 1:5000;
u = .0265;
r0 = 10;
r = r0 +u*t;
omega = .005;
phi0 = 3*pi/2;
phi = -omega*t+phi0;
x = r .* cos(phi);
y = r .* sin(phi);
plot(x,y)
grid on;
Jacob Shulman on 23 Nov 2018
where do you want it to stop? you'll have to just figure out the value of t at that point. currently you have 5000 values of t. To shorten the spiral, shorten the array t.

Jos (10584) on 23 Nov 2018
This does the job (for an integer number of turns)
% given values
pos = [8 4 ; % startpoint
2 7 ] ; % endpoint
nturns = 3 ; % number of turns (integer value)
% engine
dp = diff(pos,1,1) ;
R = hypot(dp(1), dp(2)) ;
phi0 = atan2(dp(2), dp(1)) ;
phi = linspace(0, nturns*2*pi, 10000) ; % 10000 = resolution
r = linspace(0, R, numel(phi)) ;
x = pos(1,1) + r .* cos(phi + phi0) ;
y = pos(1,2) + r .* sin(phi + phi0) ;
plot(x,y,'b-',pos(:,1),pos(:,2),'ro-') ; % nturns crossings, including end point
km meenu on 19 Jul 2020
I have a code of galaxy model and spiral line code how i draw the spiral line in the spiral arms of the galaxy

R2017b

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