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bbmatrix  Create a black-box operator from a matrix.
   BB=bbmatrix(A) encapsulates the Matlab-matrix A, full or sparse, in a
   black-box matrix. This is a handy way to treat sparse matrices, which
   are ubiquitous in large-scale computations.

   In most cases a product between a black-box operator and a
   Matlab-matrix returns a dense matrix for the sake of compatibility.
   To avoid this, all arguments should be transformed to black-box form.

   BB=bbmatrix(A,'notol') creates a black-box without estimating the
   accuracy of the product. This will reduce the construction time
   slightly, but also limits the applicable iterative algorithms.

     A=randn(1000,1); B=randn(1,1000);
     C1=A*B; C2=bbmatrix(A)*B; C3=bbmatrix(A)*bbmatrix(B);
     whos C1 C2 C3
     >>  Name      Size                   Bytes  Class
     >>  C1     1000x1000               8000000  double array
     >>  C2     1000x1000               8000000  double array
     >>  C3     1000x1000                 22071  blackbox object

   See also blackbox.