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MGH_STAGGER

MGH_STAGGER

Name


  MGH_STAGGER

Purpose


  This function is designed to be used for calculations on staggered
  rectangular grids of arbitrary dimension. It interpolates or
  extrapolates scalar values between cell centres, faces and vertices.

Category


  Finite-diffeence grids.

Calling Sequence


  Result = MGH_STAGGER(X, DELTA=delta])

Positional Parameters


  X (input, numeric array)
    An array representing values on the grid.

Keyword Parameters


  DELTA (input, integer scalar or vector)
    An integer specifying the amount by which each dimension is to
    be contracted or expanded. If DELTA is scalar, the same
    expansion/contraction is applied to every dimension. If DELTA is
    a vector, the number of elements must be greater than or equal to the
    number of dimensions in the input (greater being permitted to allow
    for omitted trailing unit dimensions).

Return Value


  The function returns a numeric array of floating, double or
  complex type, with each dimension in the input unchanged or
  expanded/contracted according to the corresponding element in
  DELTA.

Procedure


  Linear interpolation & extrapolation.
  PERFORMANCE:
  Time is propertional to number of elements and number of dimensions.
  On my Pentium 3 800 MHz machine, MGH_STAGGER times for a 2D 1-million
  element array are:
      DELTA Time (s)
        -2 0.19
        -1 0.61
          0 0.06
          1 0.88
          2 0.29

To Do


  Generalise so that DELTA can take any integer value?
###########################################################################
  This software is provided subject to the following conditions:
  1. NIWA makes no representations or warranties regarding the
    accuracy of the software, the use to which the software may
    be put or the results to be obtained from the use of the
    software. Accordingly NIWA accepts no liability for any loss
    or damage (whether direct of indirect) incurred by any person
    through the use of or reliance on the software.
  2. NIWA is to be acknowledged as the original author of the
    software where the software is used or presented in any form.
###########################################################################

Modification History


  Mark Hadfield, 1998-09:
    Written for a single dimension only.
  Mark Hadfield, 2000-12:
    Extended to multiple dimensions.
  Mark Hadfield, 2002-02:
    Fixed bug: expanding a dimension of size 2 gives wrong
    answers.
  Mark Hadfield, 2002-06:
    * DELTA can now take values in the range [-2,2].
    * Now allowing scalar DELTA to apply to all dimensions
  Mark Hadfield, 2002-07:
    Speeded code up by removing [*] subscripts from
    LHS of assignments. This improves speed by 25-50 % where
    applicable but readability suffers a bit.
  Mark Hadfield, 2002-08:
    DELTA now allowed to have more elements than the number of
    dimensions in the input.
  Mark Hadfield, 2007-02:
    Computations are now in double precision. I should really do
    this in a more flexible way!



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