- Any guidance on it is much appreciated!

- I do not know what I can do if I no tf.

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darova
on 18 Nov 2019

- Any guidance on it is much appreciated!

Helpfull page: ODE45

- I do not know what I can do if I no tf.

Try tf = 5. This should work

James Tursa
on 18 Nov 2019

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James Tursa
on 18 Nov 2019

Edited: James Tursa
on 18 Nov 2019

You've got two 2nd order DE's, so that means you have a 4th order system (2x2=4) and thus your state vector will contain four elements. You could define them as follows:

y = your 4x1 state vector with the following definitions

y(1) = r_r

y(2) = v_r

y(3) = r_t

y(4) = v_t

Then your derivative function outline would be:

function dy = myeqn(t, y)

% put some constants here or pass them in, e.g. mu etc.

dy = zeros(size(y));

dy(1) = y(2); % derivative of r_r is v_r

dy(2) = ___; % you fill this in from your r_r doubledot equation

dy(3) = y(4); % derivative of r_t is v_t

dy(4) = ___; % you fill this in from your r_t doubledot equation

end

For the dy(2) and dy(4) code, you will need to calculate your gamma value from the y vector. You could either hardcode the other stuff (D, L, m, etc.) or pass them in as input arguments. To start with, you will need to define initial values for all four states, not just v0. Also, I would have expected to see a factor somewhere on the r_t double dot equation based on the atmospheric density (a function of altitude), but I don't see it ... and this seems suspicious to me.

James Tursa
on 18 Nov 2019

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