code: def kernel_ssk_string(
      fm_train_dna=traindat, fm_test_dna=testdat, maxlen=1, decay=1
  ):
      feats_train = sg.create_string_features(fm_train_dna, sg.DNA)
      feats_test = sg.create_string_features(fm_test_dna, sg.DNA)
  
      kernel = sg.create_kernel(
          "SubsequenceStringKernel", maxlen=maxlen, decay=decay
      )
      kernel.init(feats_train, feats_train)
  
      km_train = kernel.get_kernel_matrix()
      # print(km_train)
      kernel.init(feats_train, feats_test)
      km_test = kernel.get_kernel_matrix()
      # print(km_test)
      return km_train, km_test, kernel
  
label_desc: Use image node_id 1 for calling a global function with example usage: kernel_ssk_string(fm_train_dna, fm_test_dna, maxlen, decay) and returns: km_train,  km_test,  kernel