SPIN 2018 / 2019 Exercise

Prerequisites

Make sure you have a version of git and python 2.7 installed and have a github account

Download

First obtain a copy of the current Einstein Toolkit website and tool to transfer trac tickets to github:

git clone git@bitbucket.org:einsteintoolkit/www.git einsteinwebsitegit clone

mpute the array of energies and store the results in energy[index]. Add code to WaveMoL_Energy that

Exercise

Open the file arrangements/CactusExamples/WaveMoL/src/WaveMoL.c which contains the C code used to compute phi and a quantity called energy. Find the function WaveMoL_Energy which is located at the end of the file. The function is called once per timestep and computes a quantity energy which is always positive (or zero). The loops

for (k=0; k<cctk_lsh[2]; k++)
{
  for (j=0; j<cctk_lsh[1]; j++)
  {
    for (i=0; i<cctk_lsh[0]; i++)
    {
      index = CCTK_GFINDEX3D(cctkGH,i,j,k);
      energy[index] = phit[index]*phit[index] +
        phix[index]*phix[index] +
        phiy[index]*phiy[index] +
        phiz[index]*phiz[index];
    }
  }
}

compute the array of energies and store the results in energy[index]. Add code to WaveMoL_Energy that

computes the maximum value of energy[index]
writes this value as a function of time to a file energy_maximum.xg using the same format as phi_maximum.xg . Time is accessible as the variable cctk_time .

Please compile the code once more, run it and send me the modified source file as well as energy_maximum.xg to me before the interview.

./simfactory/bin/sim build --mdbkey make 'make -j2' 
exe/cactus_sim arrangements/CactusExamples/WaveMoL/par/gaussian.par

Hint

You can access the value of phi as phi[index] and check that your code produces the same results as found in phi_maximum.xg.

If you prefer to use C++ instead of plain C you can rename the file WaveMoL.c to WaveMoL.cc, update the file arrangements/CactusExamples/WaveMoL/src/make.code.defn to list WaveMoL.cc and recompile.

This fragment outputs time:

printf("Current time: %g\n", cctk_time);

Solution

If you get stumped with the exercise, here's a worked out solution. Obviously you cannot send me this one before the interview .

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