Re: [eigen] Implementation of M.transpose()*M & M*M.transpose() |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] Implementation of M.transpose()*M & M*M.transpose()*From*: joel falcou <joel.falcou@xxxxxx>*Date*: Sun, 21 Feb 2010 14:22:52 +0100

Jinglei Hu wrote: > Hi Aron, > > Are you saying that it's better to represent the data of a Matrix by > 1D array or pointer instead of 2D array or ptr-to-ptr? If so, then > every time one wants to fetch an element A(i,j) he has to do > A[i*num_cols()+j]. Is this still more efficient than > double-dereferencing of ptr-to-ptr? > > Cheers, > Jinglei Way to access and store data is not the problem, the problem is the fact that each memory reference has to be either fetched form L2 cache or from main memory if it is not. Large numbers of techniques exists to limit the number of time data are fecthed from main memory as it is very costly. Blocking and other stuff for example. Doing a simple loop nest is usually not friendly with cache. -- ___________________________________________ Joel Falcou - Assistant Professor PARALL Team - LRI - Universite Paris Sud XI Tel : (+33)1 69 15 66 35

**References**:**[eigen] Implementation of M.transpose()*M & M*M.transpose()***From:*Jinglei Hu

**Re: [eigen] Implementation of M.transpose()*M & M*M.transpose()***From:*Gael Guennebaud

**Re: [eigen] Implementation of M.transpose()*M & M*M.transpose()***From:*Jinglei Hu

**Re: [eigen] Implementation of M.transpose()*M & M*M.transpose()***From:*Gael Guennebaud

**Re: [eigen] Implementation of M.transpose()*M & M*M.transpose()***From:*Jinglei Hu

**Re: [eigen] Implementation of M.transpose()*M & M*M.transpose()***From:*Aron Ahmadia

**Re: [eigen] Implementation of M.transpose()*M & M*M.transpose()***From:*Jinglei Hu

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