`axis`

.Adds a 1-sized dimension at index `axis`

.

`k_expand_dims(x, axis = -1)`

A tensor with expanded dimensions.

- x
A tensor or variable.

- axis
Position where to add a new axis (axis indexes are 1-based). Pass -1 (the default) to select the last axis.

This function is part of a set of Keras backend functions that enable lower level access to the core operations of the backend tensor engine (e.g. TensorFlow, CNTK, Theano, etc.).

You can see a list of all available backend functions here: https://tensorflow.rstudio.com/reference/keras/index.html#backend.