Unwieldy CvMat* in ANN using OpenCV

Question

I'm trying to use OpenCV to train a neural network in C++.

I can't convert between cv::Mat* (or Mat*, if namespace cv is used) to CvMat*, and I would appreciate some help with this.

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Let me elaborate:

I've got two data structures of cv::Mat* type. The first is the set of feature vectors and the second is the set of expected output.

   cv::Mat *feat = new cv::Mat(3000, 100, CV_32F, featureData);
   cv::Mat *op = new cv::Mat(3000, 2, CV_32F, expectedOutput);

(These are 3000 data points of feature vector length = 100 and output state = 2)

These two matrices had been populated with data of correct dimensions and seem to be working fine when sample data were printed on the console.

The neural network has been initialized as:

   int layers_array[] = {100,200,2};    //hidden layer nodes = 200

   CvMat* layer = cvCreateMatHeader(1, 3, CV_32SC1); 
   cvInitMatHeader(layer, 1,3,CV_32SC1, layers_array);

   CvANN_MLP nnetwork;
   nnetwork.create(layer, CvANN_MLP::SIGMOID_SYM, SIGMOID_ALPHA, SIGMOID_BETA);

Now, the train method of ANN is of the following template:

   virtual int train( const CvMat* inputs, const CvMat* outputs,
                       const CvMat* sampleWeights, const CvMat* sampleIdx=0,
                       CvANN_MLP_TrainParams params = CvANN_MLP_TrainParams(),
                       int flags=0 );

I tried to convert between cv::Mat * and CvMat * using the following code:

   CvMat featMat,opMat;

   (&featMat)->cols = feat->cols;
   (&featMat)->rows = feat->rows;
   (&featMat)->type = CV_32F;
   (&featMat)->data.fl = (float *)feat->data;


   (&opMat)->cols = op->cols;
   (&opMat)->rows = op->rows;
   (&opMat)->type = CV_32F;
   (&opMat)->data.fl = (float *)op->data;

   //setting up the ANN training parameters

   int iterations = network.train(&featMat, &opMat, NULL, NULL, trainingParams);

When I run this code, I get the following error message in my console:

**OpenCV Error: Bad argument (input training data should be a floating-point matrix withthe number of rows equal to the number of training samples and the number
of columns equal to the size of 0-th (input) layer) in CvANN_MLP::prepare_to_train, file ..\..\OpenCV-2.3.0-win-src\OpenCV-2.3.0\modules\ml\src\ann_mlp.cpp, 
line 694**

I understand the error message. However, to the best of my knowledge, I believe I haven't made a mess of the number of nodes in the input/output layer.

Can you please help me understand what is going wrong?

Answer 1

please try to avoid pointers to cv::Mat as well as CvMat* in general.

luckily, there's an overload to CvANN_MLP::train that takes cv::Mat as args, so use that instead:

   cv::Mat feat = cv::Mat(3000, 100, CV_32F, featureData);
   cv::Mat op = cv::Mat(3000, 2, CV_32F, expectedOutput);

   int layers_array[] = {100,200,2};    //hidden layer nodes = 200
   cv::Mat layers = cv::Mat (3, 1, CV_32SC1, layers_array );

   CvANN_MLP nnetwork;
   nnetwork.create(layers, CvANN_MLP::SIGMOID_SYM, SIGMOID_ALPHA, SIGMOID_BETA);

   int iterations = nnetwork.train(feat, op, cv::Mat(), cv::Mat(), CvANN_MLP_TrainParams());