How to create a plot with this code?

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BRS
BRS 2017-12-19
回答： Star Strider 2017-12-19
When trying to plot a graph nothing but the x axis and y axis are displayed in the figure. The code is for drawing the approximate path of a projectile which is experiencing drag.
close all
%constants and starting conditions
g =-9.81;
A = 0.25 * pi * (0.01512); %with 15.12mm the diameter of the projectile
ro = 1.293; %Binas' air density at 20C at sea level
c = 0.47; %drag coefficient for a sphere
B = 45; %launch angle
Xx = 0;
Xy = 1-sin(B)*0.202; %projectile-floor height in meters
Vc = 10.66; %launch speed in meters per second
Vx = sin(B)*Vc; %horizontal speed vector
Vy = cos(B)*Vc; %vertical speed vector
dt = 0.1; %timestep
m = 0.001684;%projectile mass in kilograms
awx(1) = 0;
awy(1) = 0;
dVy(1) = 0;
dVx(1) = 0;
dXx(1) = 0;
dXy(1) = 0;
Fwx(1) = 0;
Fwy(1) = 0;
t(1) = 0;
%model
while Xy >= 0
ax = awx;
Vx = Vx+dVx;
dVx = ax*dt;
Xx = Xx+dXx;
dXx = Vx*dt+0.5*ax*(dt)^2;
ay = g+awy;
Vy = Vy+dVy;
dVy = ay*dt;
Xy = Xy+dXy;
dXy = Vy*dt+0.5*ay*(dt)^2;
Vd = sqrt((Vx)^2+(Vy)^2);%sum of both speed vectors in flight
Fw = -0.5*ro*A*c*(Vd)^2;
theta = atan((Vx)/(Vy));%angle of Vd in fight
Fwy = cos(theta)*Fw;
Fwx = sin(theta)*Fw;
awx = (Fwx)/m;
awy = (Fwy)/m;
t = t+dt;
end
plot(Xx,Xy)
xlabel('x (m)')
ylabel('y (m)')
title('Projectile Path')

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采纳的回答

Star Strider
Star Strider 2017-12-19
You need to subscript and save ‘Xx’ and ‘Xy’, I created ‘Xxv’ and ‘Xyv’ to do this, and also ‘tv’ to save the time vector if you need it.
This plots:
%model
k = 1;
while Xy >= 0
ax = awx;
Vx = Vx+dVx;
dVx = ax*dt;
Xx = Xx+dXx;
dXx = Vx*dt+0.5*ax*(dt)^2;
Xxv(k) = Xx;
ay = g+awy;
Vy = Vy+dVy;
dVy = ay*dt;
Xy = Xy+dXy;
dXy = Vy*dt+0.5*ay*(dt)^2;
Xyv(k) = Xy;
Vd = sqrt((Vx)^2+(Vy)^2);%sum of both speed vectors in flight
Fw = -0.5*ro*A*c*(Vd)^2;
theta = atan((Vx)/(Vy));%angle of Vd in fight
Fwy = cos(theta)*Fw;
Fwx = sin(theta)*Fw;
awx = (Fwx)/m;
awy = (Fwy)/m;
t = t+dt;
tv(k) = t;
k = k + 1;
end
plot(Xxv,Xyv)
xlabel('x (m)')
ylabel('y (m)')
title('Projectile Path')
You likely still have some work to do on this.

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