[FieldTrip] lead field Cholesky....

RICHARDS, JOHN RICHARDS at mailbox.sc.edu
Sun Feb 15 06:27:01 CET 2015

I am just starting to try field trip, and want to do EEG/ERP source modeling with FEM models.  I am trying to create a FEM model with the simbio method.  I am following the tutorial: http://fieldtrip.fcdonders.nl/development/simbio.  I have a fully segmented head model (gm, wm, csf, eyes, skull,….) and get almost all the way through the methods; including seeing figures that suggest things are going in correctly.  At the last step to prepare the lead field, I get the following output (and error): Could not compute incomplete Cholesky-decompositon. Rescaling stiffness matrix  (full output below). I understand in principle the Cholesky-decomposition and why it is used, the rescaling, where this is happening in the sb_solve.m, etc  However, I don’t know what to do with my model to get this to work.  I have tried a simpler model (fewer segments), a smaller head (full head, vs MNI-type-size head), and a few other things, none of them work.

Any help on this?


using headmodel specified in the configuration
using electrodes specified in the configuration
Find electrode positions...
Calculate transfer matrix...
Electrode 2 of 128
Scaling stiffnes matrix...
Could not compute incomplete Cholesky-decompositon. Rescaling stiffness matrix…

error using ichol
Input must be structurally nonsingular with structurally nonzero diagonal.

Error in sb_solve (line 33)
    L = ichol(L);

Error in sb_calc_vecx (line 12)
vecx = sb_solve(stiff,vecb);

Error in sb_transfer (line 40)
    transfer(i,:) = sb_calc_vecx(vol.stiff,vecb,vol.elecnodes(1));

Error in ft_prepare_vol_sens (line 500)
      vol.transfer = sb_transfer(vol,sens);

Error in prepare_headmodel (line 94)
[vol, sens] = ft_prepare_vol_sens(vol, sens, 'channel', cfg.channel, 'order',

Error in ft_prepare_leadfield (line 137)
[vol, sens, cfg] = prepare_headmodel(cfg, data);

John E. Richards Carolina Distinguished Professor
Department of Psychology
University of South Carolina
Columbia, SC  29208
Dept Phone: 803 777 2079
Fax: 803 777 9558
Email: richards-john at sc.edu<mailto:richards-john at sc.edu>
HTTP: jerlab.psych.sc.edu

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