... | ... | @@ -17,6 +17,12 @@ This page summarizes all major changes and improvements to Cloudy that will be i |
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## Improved physics and numerical methods
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A version of the GTH Algorithm
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[[Grassman, Taksar, & Heyman (1985)](https://www.scirp.org/(S(lz5mqp453edsnp55rrgjct55))/reference/referencespapers.aspx?referenceid=19411);
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[Zhao (2020)](https://arxiv.org/abs/2101.11657)],
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which guarantees the positivity of equilibrium solutions of Markov chains by a specific ordering of operations in Gaussian elimination, has been applied to the atomic level solver in cases where there are no outside sources from other ionization states or chemical processes. This has addressed an infrequent, but longstanding, code failure mode where negative level abundances were predicted in species such as Ca I, and has in general been found to give more accurate results for levels with trace populations.
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## Other changes
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