decompose.h

The Spectral Toolkit is a C++ spectral transform library written by Rodney James and Chuck Panaccion

//
// spectral toolkit 
// copyright (c) 2005 university corporation for atmospheric research
// licensed under the gnu general public license
//

#ifndef __decompose__
#define __decompose__

namespace spectral
{
  /// Decomposition function template.  Partitions a list of items linearly
  /// with remainders distributed evenly.
  /// \param n length of list
  /// \param size number of partitions
  /// \param rank index of parition in \f$ [0,n-1] \f$
  /// \param length partition length (output)
  /// \param offset partition offset relative to zero (output)

  template<typename T> 
  void decompose(T n,T size,T rank,T& length,T& offset)
  {
    T remainder=n%size;
    T chunk=n/size;
    if(rank<remainder)
      {
	length=chunk+1;
	offset=(chunk+1)*rank;
      }
    else
      {
	length=chunk;
	offset=(chunk+1)*remainder+(rank-remainder)*chunk;
      }
  }
}
#endif

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