Re: [eigen] How to convert a Matrix into (big) column vector

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 22.01.2012 12:16, Helmut Jarausch wrote:
> how can I cheaply convert a Matrix to a big column vector containing
> all the columns of the Matrix stacked one on top of the other
> (assuming the Matrix is in column order, of  course)

Assuming the matrix is in column order and has no strides, you can take 
the .data() pointer and generate a Map using it.

	MatrixXd mat;
	VectorXd::Map(mat.data(), mat.rows()*mat.cols());

I guess, you can even use an aligned map for that.
Alternatively, if you just want to access sole elements, you can simply 
use mat(i); to access the i^th element (similar as in Matlab).

Actually, instead of the last, I would prefer if there was a method 
..asVector() which generates a Map as above (and automatically decides if 
the data is aligned).
Question would be, if .asVector() can also be implemented for 
Block-types and strided maps somehow.


Christoph




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Dipl.-Inf. Christoph Hertzberg
Cartesium 0.051
Universität Bremen
Enrique-Schmidt-Straße 5
28359 Bremen

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