indeed, my drawing was false. I'm not very good with ascii art. I wanted to split in 3 with the rows not the column, but the problem remains the same :-)

In fact, I use indirect_array to generate my submatrices now and it works pretty well.

So finally, in order to be a little bit matlab like (in my case it would be very convenient) can I do the following, I didn't find anything that allow to do that directly from the library:

(1) initialize an indirect_array with a vector<int> or something like that,

(2) initialize an indirect_array and do some kind of composition with range like

indirect_array ia(range1, range2, range3, ... etc)

and last but not least in order to better understand how ublas works:

- what is the difference between matrix& , matrix_expression& and matrix_reference

Thanks for your help. Very appreciated.

Cheers,

David

On Wed, Nov 18, 2009 at 20:33, Gunter Winkler <guwi17@gmx.de> wrote:

Hello David,

please read below:

David Bellot schrieb:

> Hi Ublas users,This looks like you split the matrix into 3 sets of columns and the

>

> this is a newbie question:

>

> I am implementing a cross validation algorithm and for that purpose I

> need to split up a big matrix X1 and a big vector Y1 many times in

> different way. The idea is to use a percentage of the initial dataset

> (X1 and Y1) to fit a model and the rest of this dataset to test it.

>

> Let's say my fitting procedure is

>

> double fit(const matrix<double>& X, const vector<double>& y)

>

> and initially I have my big dataset defined as

> matrix<double> X1;

> vector<double> Y1;

>

> during the loop of the cross-validation algo, I split up X1 and Y1 in

> the following manner to obtain a Xtraining and Ytraining dataset and

> Xtest and Ytest dataset:

>

> |------------------------------------|

> | Xtraining | Xtest | Xtraining |

> | | | |

> | | | |

> |------------------------------------|

>

> |------------------------------------|

> | Ytraining | Ytest | Ytraining |

> |------------------------------------|

vector into 3 sets of corresponding elements.

>Why do you need a copy? The indirect_array a able to select a set of

> Of course, Xtest and Ytest is at a different position at each step of

> the loop.

> Xtest and Ytest are easy to obtain with a matrix_range<matrix<double> >

> However Xtraining and Ytraining require a copy of the data to a

> temporary matrix (and vector).

columns and rows from a matrix.

mfg

>

> So how can I do that efficiently (indirect_array ? other ?) and do I

> need to redefine the prototype of my fit function ?

>

Gunter

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David Bellot, PhD

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http://david.bellot.free.fr