updated doc about blas.

doc/install.txt

@@ -89,14 +89,20 @@ In csh:
 Troubleshooting: Make sure you have a BLAS library
 -----------------------------------------------------
 
-Theano currently depends on having a BLAS library to link against.  The
-default is to use the blas installation information in numpy: 
-``numpy.distutils.__config__.show``, but if numpy is not configured
-[correctly] for using a fast BLAS, you should tell Theano which BLAS to use
-via the THEANO_FLAGS environment variable, or a ``.theanorc`` file. 
-
-The .theanorc file is the simplest way to set a relatively permanent option
-like this one.  Add a ``[blas]`` section with an ``ldflags``
+Their is many way to configure blas for theano. This is done with the 
+theano flags blas.ldflags (:ref:`libdoc_config`). The default is to use
+the blas installation information in numpy: 
+``numpy.distutils.__config__.show``. You can tell theano to use a different
+version if you want faster speed in case you didn't compile numpy with a 
+faster version of blas or if numpy was compiled with a static library of blas
+as this is not nupported in theano.
+
+The short way to configure the theano flags blas.ldflags is by setting the
+env variable THEANO_FLAGS to blas.ldflags=XXX
+(in bash export THEANO_FLAGS=blas.ldflags=XXX)
+
+The ${HOME}/.theanorc file is the simplest way to set a relatively permanent
+option like this one.  Add a ``[blas]`` section with an ``ldflags``
 entry like this:
 
 .. code-block:: text
@@ -108,12 +114,39 @@ entry like this:
 
     # other stuff can go here
 
-If you prefer to use an environment variable, type something like this: ``export THEANO_FLAGS="blas.ldflags=<gcc linker flags>"`` 
-so maybe ``export THEANO_FLAGS="blas.ldflags=-lf77blas -latlas -lgfortran"`` might work for you.
-
 For more information on the formatting of ~/.theanorc and the configuration options that you can put there, 
 see :ref:`libdoc_config`.
 
+Here are some different way to configure it:
+
+0) Do nothing and use the default config. It don't work in the case numpy was
+compiled with a static library. ATLAS is compiled by default only as a static lib.
+
+1) The simplest case is too disable the usage of the blas library. In that
+case, we call numpy. If numpy is linked with a fast
+implementation of blas, it will be faster in theano, but not as fast if 
+linked directly in theano in some case(for gemm operation). To use numpy,
+put the value of blas.ldflags to the empty string
+(ex: export THEANO_FLAGS=blas.ldflags=).
+
+2) You can install the default version of blas if the numpy version don't work. 
+If you have root or sudo access in fedora you can do 'sudo yum install blas blas-devel'.
+Under Ubuntu(Debian too?) 'sudo apt-get install libblas-dev'. Then put the
+theano flags blas.ldflags=-lblas. Not that the default version of blas is not uptimized.
+Using an optimized version that be up to 10x faster in the blas function that we use.
+
+3) Install the ATLAS library. ATLAS is an open source optimized version of BLAS.
+You can install precompiled version on most OS, but you can compile it to have
+a faster version(I have see speed up of up to 3x, especialy on more recent computer again the precompiled one).
+in Fedora 'sudo yum install blas blas-devel'. Under Ubuntu, 
+'sudo apt-get install libblas-dev. Then use the theano flags 
+"blas.ldflags=-lblas". Then put the theano flags 'blas.ldflags' to '-lf77blas -latlas -lgfortran'
+should do it for you. But the flags value can change for each os.
+
+
+4) Use a faster version like MKL, GOTO, ... You are on your own to install it. See the
+doc of that software and put the theano flags blas.ldflags correctly.
+
 .. note::
 
     Make sure your BLAS