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<H2><A NAME="SECTION04751000000000000000">Invalid Arguments and PXERBLA</A></H2>
<P>
<A NAME="6295"> </A><A NAME="6296"> </A><A NAME="6297"> </A>
If an illegal value is supplied for one of the input arguments to
a ScaLAPACK routine, it will call the error handler PXERBLA to write
a message to the standard output unit of the form:
<PRE> ** On entry to PSGESV parameter number 4 had an illegal value</PRE>
This particular message could be caused by passing to PSGESV<A NAME="6298"> </A> a value of NRHS
that was less than zero, for example.
The arguments are checked in order, beginning with the first.
As mentioned in Chapter <A HREF="node68.html#chap2dbsd">4</A>, if an error is
detected in the <IMG WIDTH=20 HEIGHT=32 ALIGN=MIDDLE ALT="tex2html_wrap_inline19432" SRC="img736.gif"> entry of a descriptor array,
which is the <IMG WIDTH=17 HEIGHT=15 ALIGN=BOTTOM ALT="tex2html_wrap_inline19434" SRC="img737.gif"> argument in the parameter list, the
number passed to <TT>PXERBLA</TT> has been arbitrarily
chosen to be 100*<I>i</I>+<I>j</I>. This allows the user to
distinguish an error on a descriptor entry from an
error on a scalar argument.
Invalid arguments are often caused by the kind of error listed in
section <A HREF="node149.html#seccommonerrors">7.3</A>.
<P>
In the model implementation of PXERBLA<A NAME="6304"> </A> that is supplied
with ScaLAPACK, the only action that is performed is the printing of
an error message to standard output. Program execution is <EM>not</EM> terminated.
For the ScaLAPACK driver and computational routines, a RETURN statement is
issued following the call to PXERBLA. Control returns to the higher-level
calling routine, and it is left to the user to determine how the program
should proceed.
However, in the specialized low-level ScaLAPACK routines (auxiliary routines
that are Level 2 equivalents of computational routines), the call to
<TT>PXERBLA()</TT> is immediately followed by a call to
<TT>BLACS_ABORT()</TT><A NAME="6308"> </A> to
terminate program execution since recovery from an error at this level in the
computation is not possible.
<P>
It is always good practice to check for a nonzero value of INFO
on return from a ScaLAPACK routine.
<A NAME="6309"> </A>
<P>
<BR> <HR>
<P><ADDRESS>
<I>Susan Blackford <BR>
Tue May 13 09:21:01 EDT 1997</I>
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