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### [Lapack] matrix splitting problem with dstebz and sstebz

 ``` Greetings, We have discovered a problem with DSYEVX. The problem occurs for certain matrices created using a specific algorithm. We are able to work around the problem by removing the "matrix splitting" code in dstebz. This problem also occurs in sstebz. DO 10 J = 2, N TMP1 = E( J-1 )**2 !! IF( ABS( D( J )*D( J-1 ) )*ULP**2+SAFEMN.GT.TMP1 ) THEN !! ISPLIT( NSPLIT ) = J - 1 !! NSPLIT = NSPLIT + 1 !! WORK( J-1 ) = ZERO !! ELSE WORK( J-1 ) = TMP1 PIVMIN = MAX( PIVMIN, TMP1 ) !! END IF 10 CONTINUE Please see the attached test program testevx.f which demonstrates the failure. (See attached file: testevx.f) Output from the test:. *** Math check results for DSYT22 with N= 7 and M= 5 *** exceeded the threshold value of .10000000D+03 *** Math check: | U' A U - S | / ( |A| m ulp ) *** result was .76390963D+13 *** Math check: | I - U'U | / ( m ulp ) *** result was .15278193D+15 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.cs.utk.edu/private/lapack/attachments/20090629/0b84bc2a/attachment.html -------------- next part -------------- A non-text attachment was scrubbed... Name: testevx.f Type: application/octet-stream Size: 9269 bytes Desc: not available Url : http://lists.cs.utk.edu/private/lapack/attachments/20090629/0b84bc2a/testevx.obj ```
 Current Thread [Lapack] matrix splitting problem with dstebz and sstebz, Phil DeMier <= [Lapack] matrix splitting problem with dstebz and sstebz, Julien Langou

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