[row/column majority] gslclapack

Linas Vepstas linas@austin.ibm.com
Fri Mar 31 00:09:00 GMT 2006


On Thu, Mar 30, 2006 at 05:24:25PM -0500, James Bergstra wrote:
> 
> Can someone explain why we have CblasRowMajor and CblasColMajor?
> 
> I just did a little test to convince myself, and indeed (with
> -lgslcblas) the two following calls seem to produce the same answers
> in the variable c.
> 
>     cblas_dgemm(CblasRowMajor, T2, T1, ...  a, b, c)
>     cblas_dgemm(CblasColMajor, T2, T1, ...  b, a, c)
> 
> T1 and T2 are each one of CblasNoTrans and CblasTrans.
> 
> Did I make a mistake?  Are there other BLAS functions for which you
> need to specify the data format for things to work?

For matrices that are larger than the native L1, L2, and L3 caches 
on your machine (typically some dozens of KB, 1 MB and 4-16MB
respectively), you should see (possibly very large) performance
differences. Performance depends very strongly on memory access
patterns. 

--linas



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