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[SCIRUN-USERS] Re: matrix manipulation question


Chronological Thread 
  • From: David Weinstein <dmw@sci.utah.edu>
  • To: p.johnston@griffith.edu.au
  • Cc: SCIRUN Users Mailing List <scirun-users@sci.utah.edu>
  • Subject: [SCIRUN-USERS] Re: matrix manipulation question
  • Date: Wed, 20 Apr 2011 00:10:48 -0600
Hi Peter,

The CalculateFieldData module can do what you've described.  Pass in the gradient field into its Field port and the conductivity tensors (as an Nx6 NRRD) into its NRRD port.  Then set the function text-entry string on the CalculateFieldData UI to be:

RESULT = Vector(x(DATA)*xx(A)+y(DATA)*xy(A)+z(DATA)*xz(A), x(DATA)*xy(A)+y(DATA)*yy(A)+z(DATA)*yz(A), x(DATA)*xz(A)+y(DATA)*yz(A)+z(DATA)*zz(A));

I created two synthetic vectors and two synthetic tensors, stored as ASCII text files, to demonstrate this for you.  Just place the attached .txt files in a folder along-side the attached current.srn network, and then run "scirun -e current.srn" from the command-line.

Let me know if you have any questions about this or problems running it.

Cheers,
Dave


On Apr 17, 2011, at 9:57 PM, Peter Johnston wrote:

Hi All,

    I am seeking some advice regarding matrix multiplication in scirun. I have
performed some external simulations of electric fields and am using scirun
for visualisation. So, what I have is an array of points and the accompanying
hex definition file to define the mesh, the solution at the node points and the
anisotropic conductivity at the node points. I have found that I can read in the
solution and subsequently obtain the gradient of the solution at the node points.

    My question is, can I read in the conductivity matrix and multiply this by the
array of gradients to obtain the current? The conductivity matrix is Nx6 (one row
for each of the N node points) and, since the conductivity matrix is symmetric,
has rows of the form

    a11 a12 a13 a22 a23 a33

Hence the current vector at any node should be the matrix-vector product of this
matrix (expanded to 3x3) at this node and the gradient vector calculated at the node.
Is such a manipulation possible in scirun?

    Thanks for your help,

        Peter Johnston.
 
-- 
-------------------------------------------------------------------------

Assoc. Prof. Peter Johnston
Associate Professor in Applied Mathematics          Phone (07) 3735 7748
School of Biomolecular and Physical Science         Fax   (07) 3735 7773
Griffith University
Nathan
Queensland 4111
AUSTRALIA

Attachment: current.srn
Description: Binary data

0 1 2 3 4 5
1 2 3 4 5 6
0 10 20
-5 2 7

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