Error Handling

All LAPACK95 driver and computational routines have a diagnostic output argument INFO. In the case of the driver routines, this argument is optional. Three types of exit from a routine are allowed:

successful termination:

The routine returns to the calling program with INFO set to 0.

illegal value of one or more arguments, or error in memory allocation:

The routine sets INFO $< 0$ and calls the error routine ERINFO, which issues an error message identifying the first invalid argument and stops execution.

failure in the course of computation:

The routine sets INFO $> 0$ and returns to the calling program without issuing any error message. It is then the responsibility of the user to test INFO on return to the calling program.

If INFO is not supplied in the call of a driver routine and an error occurs, then the routine always issues an error message and stops execution, even when INFO $> 0$ (in which case the error message reports the value of INFO). If a user wishes to continue execution after a failure in computation, then INFO must be supplied and should be tested on return.
This behavior simplifies calls to LAPACK95 drivers when there is no need to test INFO on return and makes it less likely that users will forget to test INFO when necessary.
If an invalid argument is detected, the routines issue an error message and stop, as in LAPACK. However, in LAPACK95 there can be different reasons for an argument being invalid:

illegal value

: as in LAPACK.

invalid shape

(of an assumed-shape array): for example, a two-dimensional array is not square when it is required to be.

inconsistent shapes

(of two or more assumed-shape arrays): for example, arrays holding the right hand sides and solutions of a system of linear equations must have the same shape.

no more core allocation:

insufficient memory for LAPACK.

The value of INFO is assigned by a call to the routine ERINFO below:

SUBROUTINE ERINFO( LINFO, SRNAME, INFO, ISTAT ) 

!		  .. Scalar Arguments .. 


CHARACTER( LEN = * ), INTENT(IN) :: SRNAME 


INTEGER, INTENT( IN ) :: LINFO 


INTEGER, INTENT( OUT ), OPTIONAL :: INFO 


INTEGER, INTENT( IN ), OPTIONAL :: ISTAT 

!		.. Executable Statements .. 


IF( ( LINFO $<$ 0 .AND. LINFO $>$ -200 ) .OR. & 

( LINFO $>$ 0 .AND. .NOT. PRESENT( INFO ) ) )THEN 


WRITE ( *, * ) 'Program terminated in LAPACK_95 subroutine ', SRNAME 


WRITE ( *, * ) 'Error indicator, INFO = ', LINFO 


IF( PRESENT(ISTAT) )THEN 


IF( ISTAT /= 0 ) THEN 


IF( LINFO == -100 )THEN 


WRITE ( *, * ) 'The statement ALLOCATE causes STATUS = ', ISTAT 


ELSE 


WRITE ( *, * ) 'LINFO = ', LINFO, ' not expected' 


END IF 


END IF    


END IF 


STOP 


ELSE IF( LINFO $<=$ -200 )THEN 


WRITE(*,*) '++++++++++++++++++++++++++++++++++' 


WRITE( *, * ) '*** WARNING, INFO = ', LINFO, ' WARNING ***' 


IF( LINFO == -200 )THEN 


WRITE( *, * ) 'Could not allocate sufficient workspace for the optimum' 


WRITE( *, * ) 'blocksize, hence the routine may not have performed as' 


WRITE( *, * ) 'efficiently as possible' 


ELSE 


WRITE( *, * ) 'Unexpected warning' 


END IF 


WRITE( *, * ) '++++++++++++++++++++++++++++++++++' 


END IF 


IF( PRESENT( INFO ) ) INFO = LINFO 


END SUBROUTINE ERINFO

The use of ERINFO, INFO and LINFO is illustrated in the code in Section 3.7.