In libsvm the polynomial kernel is defined in the following way:

(gamma*u'*v + coef0)^degree).

What is the meaning of gamma in the poly kernel? In our exercise the polynomial kernel only contains the parameters coef0 and degree (and C). There is no reference to a gamma parameter.

I have guessed the value 1 to gamma (no effect when multiplying the inner product) but I am not sure because its purpose is not clear for me in the poly case.

If we do not assign any values, the default value given by libsvm is 1/# features. In our case,it will be 1/2.

Any clarifications about this gamma in poly is appreciated