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solving ode equation using ode45

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nadeeshani Haggalla
nadeeshani Haggalla on 18 Feb 2021
Edited: David Goodmanson on 20 Feb 2021
I have an ode which I need to solve with respect to the time variable.
I have 2 seperate scripts, one contains the function and the other contains the command.
my function is,
===================================
function dy_dt=func(t,y)
dy_dt=0.003445*((y-0.072)/y^3)^0.5;
end
===================================
In the other script I have,
===================================
clc, clear, close all
time=0:0.05:8.5;
[t,y]=ode45(@myfun1,time,0.073);
plot(t,y(:,1));
==================================
When the initial value for y=0.072 I get the following graph;
because y=0.072 leads to an erroneous graph I decided to give y=0.073 as the initial value for which I got the following graph;
This is also erroneous as this is not the result I expect. The graph I expect is attached below.
Can someone assist me on what errors I have done in my code? Thank you very much.
  12 Comments
David Goodmanson
David Goodmanson on 20 Feb 2021
I agree about clarification from the OP, who wrote "When the initial value for y=0.072 I get the following graph" but who also later wrote "I decided to give y=0.073 as the initial value" so it did not appear to me that the initial value = y0 was set in stone.

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Answers (1)

David Goodmanson
David Goodmanson on 19 Feb 2021
Edited: David Goodmanson on 20 Feb 2021
Hi nadeeshani,
UPDATED ANSWER
This is a speculative answer, but perhaps you did not take the square root when you calculated the constant. At any rate, plugging in sqrt(.003445) = 0.0587 in place of .003445 (NOTE: and using initial value 0.073) gives a plot that is very close to the expected one.

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