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Euler's Method using a for loop

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Peter Bohlen
Peter Bohlen on 21 May 2024 at 21:09
Commented: Les Beckham on 21 May 2024 at 21:36
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))

Accepted Answer

Les Beckham
Les Beckham on 21 May 2024 at 21:22
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
  2 Comments
Peter Bohlen
Peter Bohlen on 21 May 2024 at 21:31
Thank you very much for your help!!!
Les Beckham
Les Beckham on 21 May 2024 at 21:36
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

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