title: FSL FIX CLASSIFIER error: error: inv(): matrix appears to be singular
body: <p>I am trying to use FIX (<a href="https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FIX" rel="nofollow noreferrer">https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FIX</a>) to denoise my functional MRI data, but after running the command to train the classifier:</p>
  <pre><code>/usr/local/fix/fix -t classifier_name -l &lt;path I manually classified&gt;
  </code></pre>
  <p>I get these errors:</p>
  <pre><code>/usr/local/fix/fix -t WP2a_classifier_training -l 
  sub-01/ses-w01pol03day01Pre/func/swsub-01_ses-w01pol03day01Pre_task-joystickPre_bold.ica
  FIX Training classifier with output training file: ./WP2a_classifier_training and Melodic outputs list: sub-01/ses-w01pol03day01Pre/func/swsub-01_ses-w01pol03day01Pre_task-joystickPre_bold.ica
  copy true labels and features into training directory
  FIX features not already generated, so creating them now.
  FIX Feature extraction for Melodic output directory: sub-01/ses-w01pol03day01Pre/func/swsub-01_ses-w01pol03day01Pre_task-joystickPre_bold.ica
  create edge masks
  run FAST
  registration of standard space masks
  
  error: inv(): matrix appears to be singular
  
  terminate called after throwing an instance of 'std::runtime_error'
  what():  inv(): matrix appears to be singular
  /usr/local/fix/fix_0c_reg_masks: line 32: 26064 Aborted                 (core dumped) convert_xfm -omat $folders/fix/std2highres.mat -inverse $folders/fix/highres2std.mat
  Could not open matrix file sub-01/ses-w01pol03day01Pre/func/swsub-01_ses-w01pol03day01Pre_task-joystickPre_bold.ica/fix/std2highres.mat
  Cannot read input-matrix
  Could not open matrix file sub-01/ses-w01pol03day01Pre/func/swsub-01_ses-w01pol03day01Pre_task-joystickPre_bold.ica/fix/std2exfunc.mat
  
  error: matrix multiplication: incompatible matrix dimensions: 4x4 and 0x0
  </code></pre>
  <p>Any tip would be helpful as I'm quite stuck with this.</p>
  <p>EDIT:</p>
  <p>I am referring to this program <a href="https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FIX" rel="nofollow noreferrer">https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FIX</a></p>
  <p>Thanks.</p>