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bbblktoep1s  Create sparse/small block-Toeplitz type-1 operator.
   A block-Toeplitz operator of type-1 is a matrix which can be written
   on the form:
     BB=[U0, U1, U2, ...
         L1, U0, U1, ...
         L2, L1, U0, ...

   When many blocks are zeros, or there is limited number of blocks,
   Fourier methods may be inefficient compared to direct evaluation.
   In this case bbblktoep1s is appropiate.

   BB=bbblktoep1s(U,L) constructs the operator, where U and L are cell
   arrays containing the U- and L-blocks:
     U={U0, U1, U2, ...}
     L={L1, L2, L3, ...}

   A block can be a black-box operator, a Matlab matrix or an empty
   matrix. An empty matrix is equivalent to a zero block.

   ALGORITHM: products are evaluated directly. However, the evaluation
   is blocked, and is rich in matrix-matrix multiplications, which
   makes it reasonably efficient.

   See also bbtoeplitz, .