Sparse Inner Products

   load '\ijs\sparsemm.ijs'

   NB. d sa s - random sparse array with 
   NB.          density d and shape s

   x=: 0.0001 sa 2$1e5
   y=: 0.0001 sa 2$1e5

   $ x             NB. shape of x
100000 100000
   */ $ x          NB. # of elements in x
1e10
   
   z=: x +/ .*y    NB. inner product of x and y
   $ z             NB. shape of z
100000 100000
   
   +/ +./"1 x~:0   NB. # of nonzero rows    in x
99995
   +/ +./   y~:0   NB. # of nonzero columns in y
99995
   +/@, z~:0       NB. # of nonzero entries in z
9989822