Hi,

I need to do some maths and

__write__ about it.

Among other things, I am using linear combinations of matrices:

I tried to write this as a multiplication involving the matrices and a vector

, and possibly an intervening auxiliary big matrix with strategically placed ones and zeros, but it seems impossible.

Another example is adding, to each column of a matrix, a different linear combination of the columns of another matrix. There is more such unconventional reshuffling of matrix entries.

I can program all of this in SciLab, and it's feasible if burdensome. What I am having serious trouble with is describing all of this in proper mathematical notation.

I do not want to keep writing things with words like,

*let us define as a column vector with all the elements of matrix stacked in such-and such order*. It feels messy and confusing.

So, how can I say the same thing (rearranging a matrix into a long vector) in a nice neat clear formula? And is there a notation to do the opposite: take a long vector of, say, 16 elements, and rearrange them into a 4*4 matrix? Or for any other stuff I have mentioned here?

Thanks in advance,

Leszek.