[eigen] User defined reductions |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx
*Subject*: [eigen] User defined reductions
*From*: Douglas Bates <bates@xxxxxxxxxxxxx>
*Date*: Fri, 2 Mar 2012 08:41:53 -0600
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In the documentation for Eigen 3.1, Tutorial page 7 on Reductions
makes a brief mention of user defined reductions and suggests looking
at the DenseBase::redux() function.
My immediate goal is to determine the column-wise medians of an array.
It would be convenient if I could write it as
A.colwise().median()
but I suspect that won't be possible because the median cannot be
calculated sequentially and it appears that redux implies, well, a
reduction in the sense of MapReduce. (Evaluating the median requires
at least a partial sort of the vector.)
I can write the calculation in a loop over the columns - I just wanted
to confirm that there was not a more compact way of expressing this.