[numerics] add comment for ABCD format in MCLP
* \f$ u, w_{1}\f$ are vectors of size n.
* \f$ v, w_{2}\f$ are vectors of size m.
*
- * ABCD format:
+ * ABCD format (see "R. W. {Cottle} and J. {Pang} and R. E. {Stone}", "The Linear Complementarity Problem, Academic Press, Inc., 1992, Section 1.5 )
* \left[
* \begin{array}{cc}
* A & C \\
