ODE System Solution Maple: Plotting Earth's Orbit with Sun at Origin

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Discussion Overview

The discussion revolves around plotting the solution to a system of ordinary differential equations (ODEs) that models Earth's orbit with the Sun at the origin. Participants are examining the expected shape of the orbit and the initial conditions used in the ODEs.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about the plot generated, expecting an elliptical or circular orbit for Earth but receiving an unexpected result instead.
  • Another participant requests the code used to generate the plot to better understand the issue.
  • A third participant mentions using the ODE Analyzer and suggests that the initial conditions might be critical to resolving the problem.
  • A later reply provides an alternative set of values for the initial conditions and claims that even a simple method like Euler in Excel produces the expected plot, implying that the original setup may have issues.
  • There is a question regarding the units of the values and time used in the original equations, indicating that this could be a factor in the discrepancies observed.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the plotting issue. There are multiple competing views regarding the initial conditions and the code used, and the discussion remains unresolved.

Contextual Notes

Limitations include potential missing assumptions about the initial conditions, the dependence on the definitions of units, and unresolved mathematical steps in the ODE formulation.

Who May Find This Useful

This discussion may be useful for individuals interested in numerical methods for solving ODEs, particularly in the context of celestial mechanics and orbital dynamics.

incredibe1999
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Hey there! I was trying to plot a ODE solution, but am not getting what I should be. It is actually plotting the orbit of Earth with Sun at the origin.
My equations
upload_2018-4-5_18-53-13.png

The (-0.00011847) is GM.
The Initial Conditions:
upload_2018-4-5_18-54-10.png


The plot I get:
upload_2018-4-5_18-54-28.png

Should not I be getting a elliptic/circular plot as the orbital positions of the Earth? Also, here the period is t=1. The position is supposed to be same at t=0 and t=1. Help, please!
 

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What is the code you used to generate this plot?
 
scottdave said:
What is the code you used to generate this plot?
I used the ODE Analyzer.
 
Well, that is not very helpful for us in finding out what goes wrong.

If I use your picture (please post something one can copy as text next time -- it avoids typos) but take different values, even good old Euler in Excel gets me a plot I expect:

upload_2018-4-8_12-59-20.png


values:
Code:
dt 0,01
x_0 1
y_0 0
vx_0 0
vy_0 1
GM 1
so the expressions look OK (provided I reproduced them correctly)

Now: what are the units for your values (and for time) ?
 

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