Rosenbrock method ODE : Abrupt increase during First iteration

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SUMMARY

The discussion focuses on the application of the Rosenbrock method for solving ordinary differential equations (ODEs) related to elemental abundances during Big Bang Nucleosynthesis. The user initially attempted to solve only the first two equations by excluding components from the remaining four. Initial conditions were set to thermal equilibrium values, which contributed to the successful resolution of the problem, albeit unexpectedly. The user expressed gratitude for the assistance received in the forum.

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  • Research the Rosenbrock method implementation in numerical analysis tools like MATLAB or Python's SciPy library
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gurbir_s
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I am using Rosenbrock4 method from Odeint library in C++ to solve a set of differential equations. However, I see that it gives an unusual change in the result for first iteration but afterwards, gives good results. How can I solve it?
The set of equations is
1682164625015.png

I have first tried to solve only first two equations (removing the components of other 4 equations from them.)

This is the output, where first column is the time, 2nd - X_p, and 3rd - X_n

1682164726299.png
 
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How are you setting your initial conditions for this solution?
 
berkeman said:
How are you setting your initial conditions for this solution?
The ##X_i##'s are elemental abundances during Big Bang Nucleosynthesis. I set the initial conditions equal to their thermal equilibrium values at that point.

I don't know how, but the problem got solved automatically while I was trying to solve another problem. Idk how. Thanks for your reply.
 
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