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A recent project coordinated by the Stockholm Observatory consists in comparing the behavior of different hydrocodes on simple planet-disk problems. Namely, there are four such problems, involving respectively a Jupiter mass planet and a planet of one tenth of a Jupiter mass (called for short ‘Neptune’) embedded either in a viscous or in a inviscid disk. FARGO has been run on these test problems, and the four corresponding parameters files (stockholm*.par) are provided in the distribution. FARGO was however written before the file format specifications of the EU test problem were defined, so a module which outputs the torques and inner/outer disk masses, in the format required by the Stockholm team, was recently added to FARGO (see src/stockholm.c). In order to activate this module at runtime, FARGO must be launched with the -e flag. As a result, an additional file is produced in the output directory, named torque0.dat (for the first planet; for the second one it would be torque1.dat, etc.; the EU test problems however only involve one planet at a time). Therefore, launching the EU test problem involving a Jupiter mass planet embedded in a viscous disk is done by issuing the following command in the fargo directory:

In addition to the fine grain torque sampling every 1/20th of orbit, a snapshot of hydrodynamics variables is output every orbit, in the standard FARGO format. In order to convert these raw format files to the ASCII files required by the Stockholm group, one can use the following simple IDL routine. Just copy it to the output directory, and there, from the IDL prompt, issue something like:

if, for instance, you wish to convert files output at t=10 orbits.

Note: the ’-e’ flag also activates the damping boundary conditions module (see fargo/src/Stockholm.c), overriding whatever is specified by the InnerBoundary parameter. Previous public releases of FARGO did not include this feature. Running FARGO with the ’-e’ flag therefore produces an output fully compliant with the specifications of the Stockholm’s problem.

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