Index: /issm/trunk/externalpackages/petsc/README
===================================================================
--- /issm/trunk/externalpackages/petsc/README	(revision 6857)
+++ /issm/trunk/externalpackages/petsc/README	(revision 6857)
@@ -0,0 +1,27 @@
+petsc carries a version of Blas that uses int arguments (int32) type, while 
+Matlab carries a version of Blas that uses int64_t arguments (hidden behing 
+a ptrdiff_t type (check MATLAB_DIR/extern/include/blas.h). 
+In serial mode, Matlab discards the Petsc Blas library (even when it was statically 
+linked against the mex files!) symbols, and replaces them with its version. 
+Because the prototypes conflict (32 vs 64), crashes ensue whenever using a Blas 
+routine (for ex: VecAXPY calls BLASaxpy_, which calls daxpy). 
+
+To avoid that, we have to recompile Petsc with a 64 bit prototype. Luckily, 
+Petsc did a good job, and hid the Blas int type into the typedef BLASint (check
+in include/petsc.h). Just typedef it back from int to int64_t, and recompile, 
+and that does the trick. Don't forget the #include "inttypes.h" at the top of petsc.h,
+otherwise, crashes during the compile.
+
+Same problem may arise for using the lapack library.
+
+Now, Petsc pretends it can compile in --with-64-bit-pointers. That sets PetscInt to long long 
+The only problem, it says MUMPS, Scalapack, blacs, Plapack don't support 64 bit indexing. 
+Mumps looks like it might. 
+
+If compiling --with-64-bit-pointers,  all prototypes in Petsc ask for PetscInt = long long 
+which Issm does not know. Can't compile with this option. Unless we switch to 64 bit integers 
+in ISSM. Started to put this framework into place: we now have IssmInt, IssmDouble, IssmChar 
+in types.h. They rely on ISSM_USE_64_BIT_INDEXING symbol, define in config.h, instantiated by 
+autotools with --with-64bit-pointers=1 in configure.sh
+
+Recomendation: wait until MUMPS implements 64 bit indexing. 
Index: /issm/trunk/externalpackages/petsc/install.sh
===================================================================
--- /issm/trunk/externalpackages/petsc/install.sh	(revision 6856)
+++ /issm/trunk/externalpackages/petsc/install.sh	(revision 6857)
@@ -9,5 +9,4 @@
 
 #version of petsc?
-#version='3.0.0-p11'
 #version='3.1-p7'
 version='2.3.2-p3'; #default for now! (nightly runs)