Info Catalog octave: Matrices

octave: Empty Matrices

 
 4.1.1 Empty Matrices
 --------------------
 
 A matrix may have one or both dimensions zero, and operations on empty
 matrices are handled as described by Carl de Boor in ‘An Empty
 Exercise’, SIGNUM, Volume 25, pages 2-6, 1990 and C. N. Nett and W. M.
 Haddad, in ‘A System-Theoretic Appropriate Realization of the Empty
 Matrix Concept’, IEEE Transactions on Automatic Control, Volume 38,
 Number 5, May 1993.  Briefly, given a scalar S, an M by N matrix
 ‘M(mxn)’, and an M by N empty matrix ‘[](mxn)’ (with either one or both
 dimensions equal to zero), the following are true:
 
      s * [](mxn) = [](mxn) * s = [](mxn)
 
          [](mxn) + [](mxn) = [](mxn)
 
          [](0xm) *  M(mxn) = [](0xn)
 
           M(mxn) * [](nx0) = [](mx0)
 
          [](mx0) * [](0xn) =  0(mxn)
 
    By default, dimensions of the empty matrix are printed along with the
 empty matrix symbol, ‘[]’.  The built-in variable
 ‘print_empty_dimensions’ controls this behavior.
 
  -- : VAL = print_empty_dimensions ()
  -- : OLD_VAL = print_empty_dimensions (NEW_VAL)
  -- : print_empty_dimensions (NEW_VAL, "local")
      Query or set the internal variable that controls whether the
      dimensions of empty matrices are printed along with the empty
      matrix symbol, ‘[]’.
 
      For example, the expression
 
           zeros (3, 0)
 
      will print
 
           ans = [](3x0)
 
      When called from inside a function with the "local" option, the
      variable is changed locally for the function and any subroutines it
      calls.  The original variable value is restored when exiting the
      function.
 
      See also: format XREFformat.
 
    Empty matrices may also be used in assignment statements as a
 convenient way to delete rows or columns of matrices.  Assignment
 Expressions Assignment Ops.
 
    When Octave parses a matrix expression, it examines the elements of
 the list to determine whether they are all constants.  If they are, it
 replaces the list with a single matrix constant.
 

Info Catalog octave: Matrices