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FAQ |
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Say "MAY-sa".
Yes. It is available in a variety of sizes for your convenience.
The picture shows the intense authors hard at work making final edits.
A late night session working on the paper around Bill's dining room table with a projector, a makeshift screen, and ample red wine (left to right, Frank Timmes, Aaron Dotter, Falk Herwig, Lars Bildsten, and Bill Paxton). Photo taken by Bill's patient wife, Kathlyn, who deserves a great deal of credit for the existence of MESA.
MESA is no longer supported on 32-bit systems. This isn't by design; we simply haven't been able to get it to work! So if you REALLY want to use an antique 32-bit system for MESA, you'll have to try to make it work yourself.
{% include releases.html %}
Errors like
Fatal Error: Wrong module version '7' (expected '5')
typically arise because you have changed the gfortran compiler since you last built MESA. (Sometimes a changed gfortran version is an indication that you forgot to activate the MESA SDK.) To fix, run ./clean in the MESA directory, and then try building again.
Make sure you have the option pgstar_flag = .TRUE. in the &star_job section of your input file. Also, if you're not using the SDK, make sure you enabled PGPLOT in your utils/makefile_header file (when using the SDK, PGPLOT is enabled by default).
Fortran. But MESA is written using advanced features of modern Fortran which make it very different from Fortran 77 codes you might have previously seen (or written!). If you are not already familiar with the new and wonderful things that have been added, there are good resources available on the web -- here's one: Fortran 95 language features.
"Thread-safe" simply means that users can take advantage of multicore processors.
For example, during stellar evolution, you need to evaluate the eos at lots of points:
{% highlight fortran %} do k = 1, num_zones call eos(T(k), rho(k), ....) end do {% endhighlight %}
Most fortran compilers (ifort and gfortran and others) support OpenMP, so the loop can be made to run in parallel by adding 2 lines of magic:
{% highlight fortran %} !$OMP PARALLEL DO PRIVATE (k) do k = 1, num_zones call eos(T(k), rho(k), ....) end do !$OMP END PARALLEL DO {% endhighlight %}
Now, if I have 4 cores, I'll have 4 threads of execution evaluating the eos.
However, for it to work, the implementation needs to be thread-safe.
In practice this means, making shared data read-only after
initialization. Working memory must be allocated from the stack (as
local variables of routines) or allocated dynamically (using
fortran95's allocate primitive). So, basically it boils down to
avoiding common blocks and save's. It's easy to arrange for this in
new code; it can be nasty converting old code however. Stellar
evolution is a good candidate for making use of many cores. Just
wrapping "parallel" directives around some loops does it if the system
is designed with that in mind -- and MESA is. But there is still much
to be done to make good use of more than 3 or 4 cores in
MESA/star.
It will be an ongoing effort to improve the design of
the code in that area; help with that is welcomed!
The easiest way to get the idea is to look at a sample, and in the MESA directory you will find a subdirectory called “sample”. Make a copy of the sample directory anywhere you’d like and give it whatever name you want. Follow the instructions in the README file to make and test the sample.