[Numpy-discussion] Zero row in SVD's unitary matrix on some Mac's

[Jason Grout]

On 4/26/11 3:29 PM, Pauli Virtanen wrote:
> On Tue, 26 Apr 2011 14:52:52 -0500, Jason Grout wrote:
> [clip]
>> The updated rwork calculation makes no difference with a 3x4 matrix
>> (both the old calculation and the new calculation give 66 in the 3x4
>> case), so I don't think that is affecting anything.
>
> Actually, there *is* a difference for the 3*4 matrix:
>
> 	old = 3*3*5 + 5*3 = 60
> 	new = 3*3*5 + 7*3 = 66
>
> The old calculation had 5 instead of 7 in the formula --- I don't know if
> it was written according to an older version of the documentation, or if
> was is simply a bug.


I was talking about our C example program, based on the example from 
Intel [1].  Intel already had the 3*3*5+7*3 calculation; that's what I 
called the "old" calculation.  The "new" calculation I was referring to 
was the "min(M,N)*max(5*min(M,N)+7,2*max(M,N)+2*min(M,N)+1)" calculation 
from Lapack 3.3.2.

Thanks,

Jason


[1] 
http://software.intel.com/sites/products/documentation/hpc/mkl/lapack/mkl_lapack_examples/zgesdd_ex.c.htm