Compression using Auto encoder then Classification using LDA

hello ... I have to matrices with size (175*19),(175*1) respectively, first I need to compress these two matrics to a smaller size for example (5*19), (5*1) respectively. .

. Then I will compare them using LDA >>>>

   %%%%%%%%%%%%%%%%%%%%%%%Training %%%%%%%%%%%%%%%%%%%%%%%
trainData  = ;  % (5*19)
trainData = trainData';
Lables= [1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0]; %(1*19)
Mdl = fitcdiscr(trainData,Lables);
                   %%%%%%%%%%%%%%%%%%%%%%%Testing %%%%%%%%%%%%%%%%%%%%%%%
        testData=.... %(5*1)
        testData = testData';
       result = predict(Mdl,testData);
  end

my question is how can I compress my matrics (note that the second matrix is small but I need it to be same as the size of the first).