Euler's Method using a for loop

I am trying to produce a graph of displacement vs. velocity of a falling parachuter and produce tabulated values. I have been given the function--which I have attached a screenshot of. My code is currently producing the error: "Array indices must be positive integers or logical values.

My Code:

clear all

%initial conditions

g0 = 9.81; %m/s^2

R = 6.37e6; %m

h = 10000; %Step Size in m

x = 0 : h : 100000; % Range of X values

v = zeros(size(x));

vi = 1400; %m/s Initial velocity

n = numel(v); % Number of values for velocity

for i=1:n-1

v(x(i+1)) = v(x(i)) + ((g0/v(x(i))) * (R^2/ ((R + x(i))^2))) * (x(i+1) - x(i));

end

plot (x(i),v(i))

Answer 1

[Les Beckham]

I'm not sure I believe that the equation given in your attached image is correct. However, the changes below allow the code to run so that you can work out the details.

%initial conditions 
g0 = 9.81; %m/s^2
R = 6.37e6; %m
h = 10000; %Step Size in m 
x = 0 : h : 100000; % Range of X values
v = zeros(size(x)); 
v(1) = 1400; %m/s Initial velocity <<<<< initialize the first element of v
n = numel(v); % Number of values for velocity 
for i=1:(n-1)
    v(i+1) = v(i) + ((g0/v(i)) * (R^2/ ((R + x(i))^2))) * (x(i+1) - x(i));
    % ^^-----^^----------^^------index using i rather than x(i)
end
plot (x,v) % << change to plot the entire v vector against the entire x vector
grid on

[Peter Bohlen]

Thank you very much for your help!!!

[Les Beckham]

You are quite welcome.

Also, if you are just getting started with Matlab, I would highly recommend that you take a couple of hours to go through the free online tutorial: Matlab Onramp