# [FieldTrip] Dipole time course

Rojas, Don Don.Rojas at ucdenver.edu
Fri Apr 1 20:15:00 CEST 2011

```Andreas,

I just wrote that code snippet from memory so it figures it wouldn't work without a little clean up. I forgot what the dimensions would be of the Li and Qn variables and the dot operation has to have arrays of the same size as input. I tested an example and this correction should work for you. I also corrected a parenthetic error on the use of double in the Qn line that would not have generated an error. I added a couple of transposes here and there. But, check your sizes as follows if you have problems - often, something will just need to be transposed to get it into the proper shape. I added some info on each input and variable to hopefully clarify what I'm after in the example:

source.dip.pos: 1 x 3
orientation_vector: 1 x 3 (Fieldtrip source structure orientation is 3 x 1 per dipole, so probably need to transpose if getting from source structure)
L: nchannels x 3
Li: 3 x nchannels;
Qn: 1 x 3, then 3 x nchannels after repmat()
W: 1 x nchannels
waveform: 1 x nsamples
data: Fieldtrip timelock structure with avg field
data.avg: nchannels x nsamples
vol: volume conductor in Fieldtrip - I coded this with a single sphere model
source: source output from ft_dipolefitting()

Revised code example:

Li 			= pinv(L); % pseudoinverse of L
Qn 			= double(orientation_vector/norm(orientation_vector)); % normed orientation vector
Qn 			= repmat(Qn,length(Li),1)'; % make Qn the same size as Li
W 		 	= dot(Li,Qn)'; % weights for projection to source space
waveform 	= dot(data.avg,repmat(W,1,size(data.avg,2))); % source waveform

Don

On Apr 1, 2011, at 8:37 AM, Andreas Wollbrink wrote:

> Hi Don,
>
> I just tried out your approach on how to achieve the source waveform
> based on a given dipole source but failed calculating the scalar product
> of the inverse leadfield matrix and the normed orientation vector:
>
> W = dot(Li,Qn);
>
> error message: A and B must be same size.
>
> May I ask you for a suggestion?
>
> Best,
> Andreas
>

```