The macro names \pgfmathlogtwo and \pgfmathlogten for the math functions
log2 and log10 are missing. Only the macro names with digits are available:
\csname pgfmathlog2\endcsname
\csname pgfmathlog10\endcsame
The macro names \pgfmathlogtwo and \pgfmathlogten are documented in the manual in section "90.2.1 Basic arithmetic functions".
However, \pgfmathatantwo for atan2 exists, from math/pgfmathfunctions.trigonometric.code.tex:
% This is needed since \pgfmathatan2 is not a legal macro name
\expandafter\let\expandafter\pgfmathatantwo\csname pgfmathatan2\endcsname
\expandafter\let\expandafter\pgfmathatantwo@\csname pgfmathatan2@\endcsname
Therefore I suggest the same for log2 and log10 in file math/pgfmathfunctions.basic.code.tex:
% This is needed since \pgfmathlog2 and \pgfmathlog10 are not legal macro names
\expandafter\let\expandafter\pgfmathlogtwo\csname pgfmathlog2\endcsname
\expandafter\let\expandafter\pgfmathlogtwo@\csname pgfmathlog2@\endcsname
\expandafter\let\expandafter\pgfmathlogten\csname pgfmathlog10\endcsname
\expandafter\let\expandafter\pgfmathlogten@\csname pgfmathlog10@\endcsname
