Description - cmyoo/cosmos GitHub Wiki

What can be calculated with the default settings of COSMOS

With the default setting, the time evolution of the spacetime from a specific initial curvature fluctuation can be calculated.

Calculation domain and boundary condition

$-L\leq X\leq L$, $0\leq Y\leq L$ and $0\leq Z\leq L$, where $X$, $Y$ and $Z$ are the reference Cartesian coordinates. The boundary surface $(0<X\leq L,Y=0,0\leq Z\leq L)$ is identified to the surface $(-L\leq X< 0,Y=0,0\leq Z\leq L)$ with the $\pi$ rotation around $Z$ axis

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Initial curvature perturbation profile (https://arxiv.org/abs/2403.11147)

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The corresponding parameters are found in the file par_ini.d

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Resolution

The initial resolution setting is 60 grid points for the length $L$. One can change the number of grids by changing the corresponding parameters in the file "par_ini.d"

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One may have to change the number of grids for the higher mesh refinement layers. The corresponding parameters are given in the file "par_fmr.d".

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Two additional layers will be introduced with the default setting. The parameter values indicate the number of grids in the lower layer before introducing the refined higher layer. The 2 additional layers for the mesh refinement are introduced when the value of the lapse function at the origin reduces to 0.3 and 0.15. These values of the lapse function can be controlled by the corresponding parameters in the file "par_fmr.d".

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Apparent horizon finder

Output files expected to be generated

  • "out_AHfig.dat": Shape of the apparent horizon
  • "out_AH.dat": Time evolution of geometrical variables of the apparent horizon
  • "out_jkz.dat": Variables on $z$-axis as functions of $z$
  • "out_jyl.dat": Variables on $y$-axis as functions of $y$
  • "out_xkl.dat": Variables on $x$-axis as functions of $x$
  • "out_xyl.dat": Variables on $xy$-plane as functions of $x$ and $y$
  • "out_xkz.dat": Variables on $xz$-plane as functions of $x$ and $z$
  • "out_const.dat": Time evolution of constraint violations
  • "out_all.dat": Data file that can be used as an initial data file to continue the time evolution
  • (Only for examples) "out_diff.dat": The differences from the expected values listed in "exp_jkz.dat".