Projectile motion with drag and magnus effect. So far im just trying to make it work with air resistance however I get a Index exceeds the number of array elements (1). Error in projectile_golf (line 36) vx(i)=vx(i​-1)-FdragX​(i-1)*dt;

function projectile_golf 
clear
clc
format long g;
workspace
format compact 
fontSize = 20;

g = 9.81;               % acceleration due to gravity in Y
y0 = 0;                 % intial position y
v0 = 50;                % initial velocity magnitude
Angular_w = 100         % Angular Velocity (rad/s)
angle = 30;             % angle of strike
c = 4.5*10^(-5);        % Coefficient of drag
r = 21.5*10^(-3);       % Radius of gold ball
m = 46*10^(-2);         % Mass of golf ball 
rho_air = 1.2;          % Density of air 



px(1) = 0;              % position of x initial
py(1) = y0;             % position of y initial
v(1) = v0;
vx = v0*cosd(angle);
vy = v0*sind(angle);
vx(1) = vx;
vy(1) = vy;
dt=0.1; 
t=[0:dt:100];
FdragX(1) = v(1)*vx(1)*c;  % Drag force in X direction
FdragY(1) = v(1)*vy(1)*c;  % Drag force in Y direction

for i=2:length(t)
    v(i) = sqrt((vx(i-1)^2)+(vy(i-1)^2));           % velocity magnitude
    px(i)=px(i-1)+vx(i-1)*dt;                       % new position x
    vx(i)=vx(i-1)-FdragX(i-1)*dt;                   % new velocity x
    py(i)=py(i-1)+vy(i-1)*dt;                       % new position y
    vy(i)=vy(i-1)-g*dt-FdragY(i-1)*dt;              % new velocity x
    if py<0
        i = length(t);
    end 
     
end 
figure(1);
plot(px,py);

Answer 1

[Alan Stevens]

You don't update FdragX and FdragY. You should add

    FdragX(i) = v(i)*vx(i)*c;  % Drag force in X direction
    FdragY(i) = v(i)*vy(i)*c;  % Drag force in Y direction

inside you loop.

Also, instead of trying to alter i within the loop, you might be better to use

    if py(i)<0
        break
    end