https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Extracting-U-from-getrf/m-p/1167987#M28340 <P>I'm trying to use getrf to put a MxN matrix in RREF (get U, divide by leading entry) but either I'm misunderstanding the function description or something strange is going on.&nbsp; Now my understanding is that on return A contains both U and L, and IPIV contains the pivot indices (i.e. the index of the first non-zero entry in U&nbsp;on each row) to enable you to determine where L stops and U begins within A.&nbsp; But the values being return in IPIV often don't make any sense by this interpretation, with the returned index often referring to a point before or after the "actual" start of U, and in some cases they aren't even non-decreasing (i.e. [1,3,2,4,4]).&nbsp; I've confirmed through matlab that the U and L being returned in A are correct, but I can't make any sense of IPIV and without it I'm not able to automatically extract those two matrices from the returned A.&nbsp;</P><P>Am I missing something in what IPIV is, or does anyone have some advice on what might be going wrong?</P> Tue, 21 Apr 2020 20:17:01 GMT Streuber__Gregg 2020-04-21T20:17:01Z https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Extracting-U-from-getrf/m-p/1167987#M28340 <P>I'm trying to use getrf to put a MxN matrix in RREF (get U, divide by leading entry) but either I'm misunderstanding the function description or something strange is going on.&nbsp; Now my understanding is that on return A contains both U and L, and IPIV contains the pivot indices (i.e. the index of the first non-zero entry in U&nbsp;on each row) to enable you to determine where L stops and U begins within A.&nbsp; But the values being return in IPIV often don't make any sense by this interpretation, with the returned index often referring to a point before or after the "actual" start of U, and in some cases they aren't even non-decreasing (i.e. [1,3,2,4,4]).&nbsp; I've confirmed through matlab that the U and L being returned in A are correct, but I can't make any sense of IPIV and without it I'm not able to automatically extract those two matrices from the returned A.&nbsp;</P><P>Am I missing something in what IPIV is, or does anyone have some advice on what might be going wrong?</P> Tue, 21 Apr 2020 20:17:01 GMT https://community.intel.com/t5/Intel-oneAPI-Math-Kernel-Library/Extracting-U-from-getrf/m-p/1167987#M28340 Streuber__Gregg 2020-04-21T20:17:01Z