Implemented function to compute asymptotic exponents

This PR implements functions to compute the asymptotic exponents in the form of plots and of a table of their expectation values and uncertainties at given x and Q. The definition of the asymptotic exponents is as in Eq. (4) of [arXiv:1604.00024]. Examples are provided; the functions are documented. New PDF bases have been defined to introduce PDF combinations that may be relevant for the computation of the asymptotic exponents.

validphys2/src/validphys/asy_exponents.py

@@ -123,8 +123,8 @@ def beta_asy(pdf, *,
 
     return betaGrid
 
-class AsyExponentPlotter(PDFPlotter):
-    """ Class inherenting from BandPDFPlotter, changing title and ylabel to reflect the effective
+class AsyExponentBandPlotter(BandPDFPlotter):
+    """ Class inheriting from BandPDFPlotter, changing title and ylabel to reflect the asymptotic
     exponent being plotted.
     """
 
@@ -141,10 +141,6 @@ class AsyExponentPlotter(PDFPlotter):
         else:
             return fr"$\{self.exponent}_a$ for ${parton_name}$"
 
-class AsyExponentBandPlotter(BandPDFPlotter, AsyExponentPlotter):
-    def __init__(self, exponent, *args,  **kwargs):
-        super().__init__(exponent, *args,  **kwargs)
-
 alpha_asy_pdfs = collect('alpha_asy', ('pdfs',))
 
 @figuregen