Question

I have a problem with training a model using the PASCAL dev kit with the Discriminatively trained deformable part model system developed by Felzenszwalb, D. McAllester, D. Ramaman and his team which is implemented in Matlab.

Currently I have this output error when I tried to train a 1-component model for ‘cat’ using 10 positive and 10 negative images.

Error:

??? Index exceeds matrix dimensions.

Error in ==> pascal_train at 48
models{i} = train(cls, models{i}, spos{i}, neg(1:maxneg),
0, 0, 4, 3, ...

Error in ==> pascal at 28
model = pascal_train(cls, n, note);

And this is the pascal_train file

function model = pascal_train(cls, n, note)

% model = pascal_train(cls, n, note)
% Train a model with 2*n components using the PASCAL dataset.
% note allows you to save a note with the trained model
% example: note = 'testing FRHOG (FRobnicated HOG)

% At every "checkpoint" in the training process we reset the 
% RNG's seed to a fixed value so that experimental results are 
% reproducible.
initrand();

if nargin < 3
  note = '';
end

globals; 
[pos, neg] = pascal_data(cls, true, VOCyear);
% split data by aspect ratio into n groups
spos = split(cls, pos, n);

cachesize = 24000;
maxneg = 200;

% train root filters using warped positives & random negatives
try
  load([cachedir cls '_lrsplit1']);
catch
  initrand();
  for i = 1:n
    % split data into two groups: left vs. right facing instances
    models{i} = initmodel(cls, spos{i}, note, 'N');
    inds = lrsplit(models{i}, spos{i}, i);
    models{i} = train(cls, models{i}, spos{i}(inds), neg, i, 1, 1, 1, ...
                      cachesize, true, 0.7, false, ['lrsplit1_' num2str(i)]);
  end
  save([cachedir cls '_lrsplit1'], 'models');
end

% train root left vs. right facing root filters using latent detections
% and hard negatives
try
  load([cachedir cls '_lrsplit2']);
catch
  initrand();
  for i = 1:n
    models{i} = lrmodel(models{i});
    models{i} = train(cls, models{i}, spos{i}, neg(1:maxneg), 0, 0, 4, 3, ...
                      cachesize, true, 0.7, false, ['lrsplit2_' num2str(i)]);
  end
  save([cachedir cls '_lrsplit2'], 'models');
end

% merge models and train using latent detections & hard negatives
try 
  load([cachedir cls '_mix']);
catch
  initrand();
  model = mergemodels(models);
 48:   model = train(cls, model, pos, neg(1:maxneg), 0, 0, 1, 5, ...
                cachesize, true, 0.7, false, 'mix');


save([cachedir cls '_mix'], 'model');
end

% add parts and update models using latent detections & hard negatives.
try 
  load([cachedir cls '_parts']);
catch
  initrand();
  for i = 1:2:2*n
    model = model_addparts(model, model.start, i, i, 8, [6 6]);
  end
  model = train(cls, model, pos, neg(1:maxneg), 0, 0, 8, 10, ...
                cachesize, true, 0.7, false, 'parts_1');
  model = train(cls, model, pos, neg, 0, 0, 1, 5, ...
                cachesize, true, 0.7, true, 'parts_2');
  save([cachedir cls '_parts'], 'model');
end

save([cachedir cls '_final'], 'model');

I have highlighted the line of code where the error occurs at line 48.

I am pretty sure that the system is reading in both the positive and negative images for training correctly. I have no idea where this error is occurring since matlab does not indicate precisely which index is exceeding the matrix dimensions.

I have tried to tidy up the code as much as possible do guide me if I have done wrong somewhere.

Any suggestions where I should start looking at?

Ok, I tried with the use of display to check the variables in use for pascal_train;
disp(i);
disp(size(models));
disp(size(spos));
disp(length(neg));
disp(maxneg);

So the results returned were;

 1

 1     1

 1     1

10

200

Answer 1

I don’t have an answer to your question, but here is a suggestion that might help you debug this problem yourself.

In the Matlab menu go to Debug-> Stop if Errors/Warnings … and select “Always stop if error (dbstop if error)”. Now run your script again and this time when you get the error, matlab will stop at the line where the error occurred as if you put a breakpoint there. At that point you have the whole workspace at your disposal and you can check all variables and matrix sizes to see which variable is giving you the error you are seeing.