Error in gram_matrix: K$batch_flatten(K$permute_dimensions(x, list(2L, 0L, 1L)))

[hermandr]

Hi,

I am running the vignette neural_style_transfer and I encountered this error:

for (layer_name in style_layers){
  layer_features <- outputs_dict[[layer_name]]
  style_reference_features <- layer_features[2,,,]
  combination_features <- layer_features[3,,,]
  K$clear_session()
  sl <- style_loss(style_reference_features, combination_features)
  loss <- loss + ((style_weight / length(style_layers)) * sl)
}

Error:

 Error in py_call_impl(callable, dots$args, dots$keywords) : 
  ValueError: Tensor("Const:0", shape=(1,), dtype=int32) must be from the same graph as Tensor("strided_slice_4:0", shape=(2,), dtype=int32). 
> traceback()
5: stop(list(message = "ValueError: Tensor(\"Const:0\", shape=(1,), dtype=int32) must be from the same graph as Tensor(\"strided_slice_4:0\", shape=(2,), dtype=int32).", 
       call = py_call_impl(callable, dots$args, dots$keywords), 
       cppstack = NULL))
4: py_call_impl(callable, dots$args, dots$keywords)
3: K$batch_flatten(K$permute_dimensions(x, list(2L, 0L, 1L))) at #2
2: gram_matrix(style) at #2
1: style_loss(style_reference_features, combination_features)

SessionInfo:

> sessionInfo()
R version 3.6.3 (2020-02-29)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19041)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] keras_2.3.0.0

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.5       lattice_0.20-38  zeallot_0.1.0    rappdirs_0.3.1   grid_3.6.3      
 [6] R6_2.4.1         jsonlite_1.7.1   magrittr_1.5     tfruns_1.4       whisker_0.4     
[11] Matrix_1.2-18    reticulate_1.16  generics_0.0.2   tools_3.6.3      compiler_3.6.3  
[16] base64enc_0.1-3  tensorflow_2.2.0

How do I fix this error?