issue_comments: 112811117
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| html_url | issue_url | id | node_id | user | created_at | updated_at | author_association | body | reactions | performed_via_github_app | issue |
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| https://github.com/pydata/xarray/issues/435#issuecomment-112811117 | https://api.github.com/repos/pydata/xarray/issues/435 | 112811117 | MDEyOklzc3VlQ29tbWVudDExMjgxMTExNw== | 6405510 | 2015-06-17T13:58:59Z | 2015-06-17T13:58:59Z | NONE | Thank you for your thoughts. While composing my response I realized I'm actually concerned about two distinct data representation problems. 1. Energies computed for any number of phases at discrete temperatures, pressures and compositions in a system ("energy surface data"). This is intermediate data in the computation. 2. Result of constrained equilibrium computations using the data in (1) The shape of the data in (2) would be something like (condition axis 1, condition axis 2, ..., condition axis n). Conditions can be independent or dependent variables (the solver can work backwards), and not all combinations of conditions result in an answer. For example, I want to map the phase relations of a 4-component system in T-P-x space. I choose 50 temperatures and pressures, plus 100 points per independent composition axis (here I fix the total system size so that 1 composition variable is dependent). So then the shape of my equilibrium data would be (50, 50, 100, 100, 100). But what is the value of each element, the equilibrium result? The equilibrium result is also multi-dimensional. I need to store the computed chemical potentials for each component (1-dimensional), the fraction of each stable phase (1-dimensional), and references to the corresponding physical states in the energy surface data (1-dimensional). Going back to (1), phases can also have "internal" composition variables that map to the overall composition in a non-invertible way, i.e., two physical states can have the same overall composition but different internal compositions. The way I've been handling this is by adding more columns to my DataFrames, but it's not a sustainable approach for reasons we've both mentioned. The data in (1) makes the most sense to me as a "ragged ndarray", where the internal degrees of freedom of each phase are free to be be different but still mapping to global composition coordinates. For (2), I imagine a "result object" bundled up inside all the conditions dimensions, but I need to be able to slice and search the derived/computed quantities just as easily as the independent variables. Does xray make sense for either or both of these cases? |
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