Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Variational principles and thermodynamics   Variational principles play a fundamental role in deriving evolution
equations of physics. They are working well in case of nondissipative evolution
but for dissipative systems they are not unique, not predictive and not
constructive. With methods of modern nonequilibrium thermodynamics, one can
derive evolution equations for dissipative phenomena and, surprisingly, can
also reproduce the Euler-Lagrange form of the evolution equations for ideal
processes. In this work, we examine some demonstrative examples and compare
thermodynamic and variational techniques. Then, we argue that instead of
searching for variational principles for dissipative systems, a different
program can be more fruitful: the second law alone can be an effective tool to
construct both dissipative and nondissipative evolution equations.

27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
16
The categories of this paper are: stat