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<H2><A NAME="SECTION04466000000000000000">Error Handling and the Diagnostic Argument INFO</A></H2>
<A NAME="subsecinfo"> </A>
<P>
All<A NAME="3504"> </A>
driver and computational routines<A NAME="3505"> </A>
have a diagnostic argument INFO<A NAME="3506"> </A><A NAME="3507"> </A>
that indicates the success or
failure of the computation. It is
recommended that the user always
check the value of INFO on exit
from calling a ScaLAPACK routine.
The value of INFO is defined as follows:
<P>
<UL>
<LI> INFO = 0: successful exit
<LI> INFO < 0: illegal value of one or more arguments -- no computation
performed
<LI> INFO > 0: failure in the course of
computation<A NAME="3509"> </A>
</UL>
<P>
The value of (INFO<0)<A NAME="3511"> </A>
is calculated as follows: if the error is detected
in the <I>j</I>th entry of a descriptor array, which is
the <I>i</I>th argument in the parameter list, the
number passed to the error-handling routine
<TT>PXERBLA()</TT><A NAME="3513"> </A><A NAME="3514"> </A>
has been arbitrarily chosen to be <IMG WIDTH=102 HEIGHT=26 ALIGN=MIDDLE ALT="tex2html_wrap_inline16134" SRC="img361.gif">.
This allows the user to distinguish an error
on a descriptor entry from an error on a scalar
argument.
<P>
The standard version of <TT>PXERBLA()</TT> only
issues an error message and does not halt
execution of the program. The main reason
for this behavior is that some ``errors''
are deemed recoverable and we wanted to
allow the user the flexibility to continue
program execution if certain values were
corrected. If user wish to change this
behavior and additionally halt execution
of the program, they may add a call to
<TT>BLACS_ABORT()</TT> to their version of
<TT>PXERBLA()</TT>.
<P>
If an input error (INFO<0) is detected
at a high-level routine (ScaLAPACK driver
or computational routine), it is possible
for the user to recover from such an error
and proceed with the computation. An error
message is printed by <TT>PXERBLA()</TT>, a
RETURN is issued, and the program execution
continues. However, if an error is detected
in a low-level ScaLAPACK routine, this error
is considered unrecoverable, a message is
printed by <TT>PXERBLA()</TT>, and program
execution is terminated by a call to
<TT>BLACS_ABORT()</TT><A NAME="3521"> </A>.
<P>
Likewise, if an error is detected at a
low-level routine, such as a PBLAS or
BLACS routine, this error is deemed fatal.
An error message is printed, and the
program execution is terminated by the
specific error-handling routine.
<P>
All ScaLAPACK driver and computational
routines perform global and local input
error-checking. In general, no input
error-checking is performed on the
auxiliary routines. The exception to
this rule is for the auxiliary routines
which are Level 2 versions of
computational routines (e.g., PxGETF2,
PxGEQR2, PxORMR2, PxORM2R, etc.).
For efficiency purposes, these
specialized low-level routines
perform only a local validity
check of their argument list.
If an error is detected in at
least one process of the current
context, the program execution
is stopped.
<P>
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<P><ADDRESS>
<I>Susan Blackford <BR>
Tue May 13 09:21:01 EDT 1997</I>
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