ZTFSM issues (rectangular full packed storage triangular matrix solve)

[shughey]

Hi,

I am hoping to use ZTFSM to solve a triangular system in the RPF/RFP format with and without transposition, i.e., A*X=B and A^T * x = B, where A is a triangular matrix stored in RFP format. The routine appears to function properly when trans = 'N', but when I specify trans = 'T' to solve the transpose problem A^T * X = B, I get the error "Intel MKL ERROR: Parameter 4 was incorrect on entry to ZTFSM ."

I also tried to hack around this issue by conjugating A and using trans = 'C' to denote the conjugate transpose. This results in an error on the order of 1e-3 for a 4x4 matrix.

Note that I am only changing the 'trans' flag; all other parameters remain fixed.

Am I using ZTFSM incorrectly? Is this a known bug?

Thanks

[ShanmukhS_Intel]

Hi,

Thanks for posting on Intel Communities. Kindly refer below link for usage regarding ZTFSM.

https://www.intel.com/content/www/us/en/develop/documentation/onemkl-developer-reference-fortran/top/lapack-routines/lapack-auxiliary-routines/tfsm.html

In addition, Could you please share us a sample reproducer and steps(if any), so that we could try reproducing the issue at our end.

Best regards,

Shanmukh.SS

[mecej4]

Since the MKL example files did not (?) contain a test file for the ?TFSM routines, I took the example provided by NAG and modified it for use with MKL (remove references to NAG modules, provide parameter declaration for the real kind _wp, and replace the call to x04... by a simple PRINT *,IFAIL). The program ran and produced the correct result, using the current version of IFort and MKL (OneAPI 2022).

Please provide a reproducer.

[shughey]

I think I figured out my mistake. I did not realize until reading the documentation for ZTRTTF that MKL expects the lower right triangle to be stored in conjugate-transpose form, rather than in transpose form. Things are working now. Sorry for the confusion, and thank you for the quick responses!

[Gennady_F_Intel]

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