The article says that is a contraction for , i.e., is a function of two arguments. So apparently is the derivative with respect to the second argument.
"[...] These variables give a measure of correspondence between signal and model relative to all other models, . A mechanism of concept formation and learning, an internal dynamics of the modeling fields (MF) is defined as follows,
[...]
Parameter determines the iteration step and speed of convergence of the MF system; can be interpreted as a number of signals associated with or coming from a concept object . As already mentioned, in the MF internal dynamics, similarity measures are adapted so that their fuzziness is matched to the model uncertainty. [...]"
http://www.leonid-perlovsky.com/4%20-%20Mehler.pdf (page 368)
What does it mean to take a partial derivative with respect to a model i.e. ?
Thanks in advance,
jrobot