Correct the equation for the entropy time derivative in GADGET2_SPH

This fixes #183 (closed) meaning that energy is now correctly conserved.

It also:

• Adds a parameter file and run script for the perturbed box test case.
• Adds entropy to the diagnostics file.
• Replace the MPI_AllReduce in the statistics collection by an MPI_Reduce since only rank 0 writes anyway.
• Gives a better documentation for the approx_exp() function.
• Adds an accuracy test for the approximate maths functions (currently only exp())
• Adds a test no make sure the symmetric and non-symmetric versions of the SPH interaction routines give the same answer. That was the origin of the energy non-conservation bug.

Added 3 commits:

• c73bb32d - 1 commit from branch master
• 36b22593 - Formatting
• b3947c40 - Merge branch 'master' into energy_conservation

Added 1 commit:

• 2e524c66 - New test to make sure the symmetric and non-symmetric versions of the hydro interactions work.

Title changed from Correct the equation for the entropy time derivative to Correct the equation for the entropy time derivative in GADGET2_SPH

Added 1 commit:

• 287c2882 - Use correct parameter file for PerturbedBox

Added 30 commits:

• 287c2882...bd9ec753 - 29 commits from branch master
• c406bde1 - Merged latest master branch changes

I have just updated the branch with the latest master branch changes.

Thanks, looks good to go.

mentioned in commit e29af86f

Status changed to merged