Login

News

"as.matrix" in openmx

Posted on
No user picture. Janosch Joined: 05/10/2010
Forums
OpenMx General Help
Hi everybody,
I have a simple question that might be a bit stupid. But I can't find an equivalent to the 'as.matrix' command in R. I understand that 'rvectorize' is the equivalent to 'as.vector' so I'm surprised that I can't find the 'as.matrix' thing anywhere.
Or is it maybe not yet implemented in openmx?

Thanks for your help

Greetings

Jan

Replied on Wed, 05/26/2010 - 11:11
Picture of user. mspiegel Joined: 07/31/2009

Ah right. The OpenMx backend understands only matrix types. So cvectorize() and rvectorize() resize the input matrices into (n x 1) and (1 x n) matrices. We do not have a generic resize() function that transforms an input matrix into a n x m matrix.

You could perform this transformation with a combination of the matrix subscript operator (A[x,y]), and the functions cbind() and rbind(). But perhaps we need to implement the resize function explicitly.

Log in or register to post comments
Replied on Wed, 05/26/2010 - 15:02
Picture of user. mspiegel Joined: 07/31/2009

Would it be OK to post to the forums either your script or maybe just the relevant portion that needs the matrix resize function? We're trying to get a feeling for the types of models that would need this function. If this is work in progress and you'd prefer not to put it on the forums, I would completely understand.
Log in or register to post comments
Replied on Fri, 05/28/2010 - 12:38
No user picture. Janosch Joined: 05/10/2010

Mhm I wouldn't feel too comfortable to post the whole code. But i can try to show you a bit better, where i would need the function.

I have this expression which is to be implemented in an mxAlgebra (I think its not that important what all the names stand for..):

(solve(DRIFTHATCH)%*%((EVECH%*%(exp(1%x%EVAH)-tempb)%*%solve(EVECH))-(II%x%II))%*%rvectorize(Q))

The result of that is a vector (N-variables**2 x 1).

Using square brackets indexing, I wanna refer to the elements in that vector in my 'S' matrix. But of course, in the 'S' matrix the elements are matrices. So the vector would have to be a matrix as well, in order for me to refer correctly.

What i did until now is to create two new mxMatrix objects (K and L). For two variables, they are:

K = (1,0,0,0, L = (0,0,1,0,
____0,1,0,0) ____0,0,0,1)

Now I multiply the vector (say v_vector=c(1,2,3,4)) with both of those matrices and rbind the result, so i get:

v_matrix = (1,3,
_________2,4)

This new matrix can then be used to refer to the elements in the 'S' matrix. For two or three variables this is no problem. But i wanna be able to write my skript in a way so that it can handle any number of variables. And the problem is that the matrices L and K get bigger with every variable and, even worse, that I need as many matrices as there are variables, in order to convert the vector to a matrix. So it basically becomes impossible when we are speaking of e.g. 100 variables.

So if I had a function that would do that for me I could get rid of all those K and L matrices and just use one expression.

I hope that this makes any sense in that compressed form. If you would like further information, let me know.

Greetings

Log in or register to post comments
  Login

News