http://developer.r-project.org/sparse.html http://en.wikipedia.org/wiki/matrix_representation http://www.cise.ufl.edu/research/sparse/ http://en.wikipedia.org/wiki/sparse_matrix http://www.sparsix.com/sparse.htm http://beowulf.lcs.mit.edu/18.337-2002/projects-2002/persson/18.337/fem/node6.html http://www.cstc.org/data/resources/52/sparse.htm http://osl.iu.edu/~chemuell/projects/bioinf/sparse-matrix-clustering-chrismueller.pdf http://www.patentstorm.us/patents/7197620-description.html http://www.cs.uml.edu/~lechner/datamodels2htm/sld025.htm http://rene.ma.utexas.edu/cna/itpack/manuals/user2c/node2.html http://www.google.co.uk/search?q=how+to+remove+null+element+from+sparse+matrix&hl= en&start=30&sa=n http://www.sciencedirect.com/science?_ob=articleurl&_udi=b6tyx-3xkf8092&_user=983321&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=c000044920&_version =1&_urlversion=0&_userid=983321&md5=c24b4279136c304394d2dc5874f00f98 http://delivery.acm.org/10.1145/320000/316004/p313liang.pdf?key1=316004&key2=7001607911&coll=guide&dl=guide&cfid=46062538&cftoken=99 197153 http://www.intel.com/software/products/mkl/docs/webhelp/appendices/mkl_appa_smsf.h tml