From research!csnet!CSNET-RELAY!ibm.com!CULLUMJ 7 July 1986, 13:46:36 EDT From: "JANE K. CULLUM" Received: from su-score.arpa by CSNET-RELAY.ARPA id aa11967; 7 Jul 86 15:24 EDT Return-Path: Received: from IBM.COM by SU-SCORE.ARPA with TCP; Mon 7 Jul 86 11:08:17-PDT To: na.dis%su-score.arpa@CSNET-RELAY Subject: LANCZOS CODE ReSent-Date: Mon 7 Jul 86 11:28:16-PDT ReSent-From: "Gene H. Golub" ReSent-To: MMDF-Warning: Parse error in original version of preceding line at CSNET-RELAY.ARPA ReSent-Message-ID: <12220830747.35.GOLUB@SU-SCORE.ARPA> Via: Csnet-Relay; 10 Jul 86 1:15-EDT This message is addressed to anyone of you who has obtained our LANCZOS code LEVAL from the Argonne NETLIB. This is the main program for computing eigenvalues of real symmetric matrices using our Lanczos procedure with no reorthogonalization of the Lanczos vectors. Somehow the LEVAL code which was sent to Argonne acquired two code modifications that were used for testing but which should not have been in the version being distributed to other people. One of these modifications is inconsequential in that it only affects the number of messages a user would see. However, the other modification will cause real problems if you have saved the Lanczos matrices from one run and then feed them back in to Leval on a subsequent run and try to make these matrices larger. Please fix your LEVAL code as follows: (1) The important change occurs at the point in the main program where the user calls the subroutine USPEC to initialize the user-specified matrix arrays and parameters. This statement currently reads: if(istart.eq.0) call USPEC (n,matno) It should read simply call USPEC(n,matno) (2) The message level change: Two lines prior to the CALL INVERR command which calls an inverse iteration subroutine to compute error estimates on the computed eigenvalue approximations, there is currently the statement Iwrite = 0 The flag iwrite controls the amount of information which the user sees regarding the progress of the computations. It is set by the user initially being read in from file 5. The user can in fact freely change this flag throughout LEVAL if desired. However, if you want the message level to be controlled by the value of iwrite read in from file 5, then you should remove this iwrite = 0 statement. Sorry for this problem. Please keep us informed of any problems which you encounter with this or any other of our Lanczos codes. The Hermitian codes and the singular value codes are also available from NETLIB. The complex symmetric codes or any of the other codes discussed in our book are also available but currently from us and not NETLIB. Thanks, Jane Cullum Ralph Willoughby 914-945-1589 From research!csnet!CSNET-RELAY!ibm.com!CULLUMJ 10 July 1986, 12:43:26 EDT From: "JANE K. CULLUM" Received: from su-score.arpa by CSNET-RELAY.ARPA id aa09648; 10 Jul 86 15:56 EDT Received: from IBM.COM by SU-SCORE.ARPA with TCP; Thu 10 Jul 86 12:30:29-PDT To: na.grosse%su-score.arpa@CSNET-RELAY Subject: Via: Csnet-Relay; 10 Jul 86 17:44-EDT Hi, Thanks very much for your interaction with Haldane w.r.t. our Lanczos codes. Please contact me if he has any problems with these codes. thanks, Jane Cullum