McStas Frequently Asked Questions

McStas FAQ - Frequently Asked Questions with answers

Information

Where can I get information about McStas?

A good source of information is the McStas Web page, at http://www.mcstas.org/

Where can I ask questions about McStas?

Questions about McStas should be sent to the neutron/Monte Carlo mailing list. See http://www.mcstas.org/list/ for details.

Are there any bugs in McStas?

A list of known bugs can be found at http://www.mcstas.org/documentation/problems/. Also have a look at out bug tracking system.

Installation - configuration

The installation of McStas seems rather complex. How should I proceed ?

Have a look at the Quick Install or the Official Install Instructions. We provide a Windows installer for MS Windows users, a debian package for installation on Ubuntu systems, and a dmg installer for MacOSX users. A manual installation can be done using the ./configure;make;make install procedure.
If you really can not manage, the McStas LiveDVD provides a fully functional system for all Intel/AMD based systems, without touching your local machine, but with full computing efficiency.

I have updated my system. How do I reconfigure McStas without reinstalling it ?

On Linux systems, execute (in administrator mode) the MCSTAS/tools/perl/mcstas_reconfigure script. On Windows machines, the mcconfig.pl tool can do that as well.

The installation of McStas cannot find the right Perl interpreter. What can I do?

Set the environment variable PERL to the full path of the Perl interpreter to use before running ./configure:

    rm -f config.cache              # Remove cache of old choices
    setenv PERL /full/path/to/perl5
    ./configure

See the installation instructions in the distribution for details.

How do I make PgPerl work on Red Hat/Suse/Debian/... Linux so that I can use the graphical front-ends?

In Debian, PgPerl is included in the distribution. Use dselect, synaptic, apt, or dpkg to install it from your CD or from the network.

For Red Hat Linux and other distributions that use the RPM format, binary packages might be available for the Intel i386 (IBM PC compatible) architecture at http://www.rpmseek.com.

Installing from perl-PGPLOT source migh be tedious. We have set up an automatic procedure for that (that may fail). From the McStas distribution, try a:

./configure; sudo make install-pgplot; ./configure

If you compile yourself from source code:

Make sure that PGPLOT is properly installed, including the C bindings.
On some of the old Linux distributions, the library previously called "libf2c" has been renamed to "libg2c", but PgPerl may still wrongly pick up the previous, old version. You can try to edit the makefile (after "perl Makefile.PL", but before "make") to change all occurences of "f2c" into "g2c". This problem is supposed to be fixed in a later PgPerl release (around 2.15).

Using McStas

How do I make the graphical user interface use another C compiler?

The C compiler to use, as well as any special options needed for optimization etc, can be specified during installation using the enviroment variables CC and CFLAGS. For example

    setenv CC /usr/opt/ansic/cc
    setenv CFLAGS +O
    ./configure

It may be necessary to remove the file config.cache first to override any choices made by configure during a previous install. See the installation instructions in the distribution for details. Alternatively, use

./configure --with-cc=/usr/opt/ansic/cc

It is also possible to define the MCSTAS_CC and MCSTAS_CFLAGS environement variables to override the default configuration, or to simply set it in the mcgui Preferences.

I can not write bigger files than 2Gb with McStas, is there a workaround?

First, please consider if you really need such big files. If you do, McStas can perfectly well write bigger files than 2Gb if you make sure that your MCSTAS_CFLAGS contains proper c-compiler defines to allow this. On x86 Linux with gcc, relevant values are

-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64

I think McStas gives the wrong number of neutrons in the detector in my simulation. What is wrong?

The number of neutrons histories that reach the detector in a McStas simulation is usually not very meaningful. McStas uses weighted neutrons extensively (see the manual for details) and different neutrons may carry widely different weights. Always use the intensity in detectors when analyzing simulation data.

Can McStas use clusters and Grids ?

Yes, install MPICH or OpenMPI, reconfigure McStas (see above) and select MPI or Grid when running the simulation from the GUI.

Can McStas import files from other neutron MC packages ?

Yes, McStas can read files generated by Vitess, MCNP/MCNPX, and Tripoli. Other importers are easy to write. Just ask us.

What type of data can McStas generate ?

McStas usually generates histograms (tallies) as formatted (easy to read) text files. Such text files may be read by the McStas internal plotter using PGPLOT, but also using Matlab, Scilab, VRML/HTML (web page), HDF/NeXus, XML/NeXus, Octave, IDL and more... Event files may be generated for MCNP/MCNPX, Vitess and Tripoli. McStas has also its own event file format, which can be used to split a simulation into pieces (see the User Manual with the Virtual_input/output component).

Is there a way to interact with a running simulation ?

Yes, it is possible to make the simulation report and save results during the simulation. The on-line plotting tool mcdaemon may then plot the results as they come, in the course of the computation (see the Progress_bar component). On Unix/Linux/MacOSX systems (excet when running with MPI and grids), one may additionally send USR1 and USR2 signals to the simulation (refer to the User Manual).

Kristian Nielsen
<kristian.nielsen@risoe.dk>
/
Mar 31, 1999.

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Last Modified: Tuesday, 14-Oct-2008 15:55:05 CEST