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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@389 f3b2605a-c512-4ea7-a41b-209d697bcdaa

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sjplimp
2007-03-09 15:44:22 +00:00
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@ -221,15 +221,32 @@ where it stores the system-specific *.o files.
<P>Typing "make clean" will delete all *.o object files created when
LAMMPS is built.
</P>
<P>(3) On some 64-bit machines, compiling with -O3 appears to break the
Coulombic tabling option used by the <A HREF = "pair_style.html">pair_style</A>
<I>lj/cut/coul/long</I> and <I>lj/charmm/coul/long</I> styles. By default,
tabling is used by these styles since it can offer a 2x speed-up. It
can be disabled via the <A HREF = "pair_modify.html">pair_modify</A> command.
Alternatively, the associated files (e.g. pair_lj_cut_coul_long.cpp)
can be compiled with -O2, or with the compiler flag
<I>-fno-strict-aliasing</I>. Either of those build changes seems to fix
the problem.
<P>(3) On some machines with some compiler options, the Coulomb tabling
option that is enabled by default for "long" <A HREF = "pair_style.html">pair
styles</A> such as <I>lj/cut/coul/long</I> and
<I>lj/charmm/coul/long</I> does not work. Tables are used by these styles
since it can offer a 2x speed-up. A symptom of this problem is
getting wildly large energies on timestep 0 of the examples/peptide
simulation.
</P>
<P>Here are several work-arounds. Coulomb tables can be disabled by
setting "table 0" in the <A HREF = "pair_modify.html">pair_modify</A> command.
</P>
<P>The associated files (e.g. pair_lj_cut_coul_long.cpp) can be compiled
at a lower optimization level like -O2, or with the compiler flag
<I>-fno-strict-aliasing</I>. The latter can be done by adding something
like these lines in your Makefile.machine:
</P>
<PRE>NOALIAS = -fno-strict-aliasing
</PRE>
<PRE>pair_lj_cut_coul_long.o : pair_lj_cut_coul_long.cpp
$(CC) $(CCFLAGS) $(NOALIAS) -c $<
</PRE>
<PRE>pair_lj_charmm_coul_long.o : pair_lj_charmm_coul_long.cpp
$(CC) $(CCFLAGS) $(NOALIAS) -c $<
</PRE>
<P>On a Macintosh, try compiling the pair "long" files without the -fast
compiler option.
</P>
<P>(4) Building for a Macintosh.
</P>