Add \ifdefined guard for \sl's use of \renewcommand

ml-svm.tex

@@ -1,6 +1,8 @@
 % linear svm
 \newcommand{\sv}{\operatorname{SV}} % supportvectors
+\ifdefined\sl
 \renewcommand{\sl}{\zeta} % slack variable
+\else \newcommand{\sl}{\zeta} \fi
 \newcommand{\slvec}{\left(\zeta^{(1)}, \zeta^{(n)}\right)} % slack variable vector
 \newcommand{\sli}[1][i]{\zeta^{(#1)}} % i-th slack variable
 \newcommand{\scptxi}{\scp{\thetav}{\xi}} % scalar prodct of theta and xi