Stokhos_GrowthRules.hpp

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// @HEADER
// *****************************************************************************
//                           Stokhos Package
//
// Copyright 2009 NTESS and the Stokhos contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER

#ifndef STOKHOS_GROWTH_RULES
#define STOKHOS_GROWTH_RULES

namespace Stokhos {

  template <typename value_type>
  class GrowthRule {
  public:

    GrowthRule() {}

    virtual ~GrowthRule() {}

    virtual value_type operator() (const value_type& x) const = 0;
  };
  
  template <typename value_type>
  class IdentityGrowthRule : public GrowthRule<value_type> {
  public:
    IdentityGrowthRule() {}

    virtual ~IdentityGrowthRule() {}

    virtual value_type operator() (const value_type& x) const { return x; }
  };

  template <typename value_type>
  class LinearGrowthRule : public GrowthRule<value_type> {
  public:
    LinearGrowthRule(const value_type& a_ = value_type(1), 
         const value_type& b_ = value_type(0)) : 
      a(a_), b(b_) {}

    virtual ~LinearGrowthRule() {}

    virtual value_type operator() (const value_type& x) const { return a*x+b; }

  protected:

    value_type a;

    value_type b;
  };


  template <typename value_type>
  class EvenGrowthRule : public GrowthRule<value_type> {
  public:
    EvenGrowthRule() {}

    virtual ~EvenGrowthRule() {}

    virtual value_type operator() (const value_type& x) const { 
      if (x % value_type(2) == value_type(1)) return x+value_type(1);
      return x;
    }

  };

  template <typename value_type>
  class ClenshawCurtisExponentialGrowthRule : public GrowthRule<value_type> {
  public:
    ClenshawCurtisExponentialGrowthRule() {}

    virtual ~ClenshawCurtisExponentialGrowthRule() {}

    virtual value_type operator() (const value_type& x) const { 
      if (x == value_type(0)) return value_type(0);
      return std::pow(value_type(2),x-value_type(1));
    }

  };

  template <typename value_type>
  class GaussPattersonExponentialGrowthRule : public GrowthRule<value_type> {
  public:
    GaussPattersonExponentialGrowthRule() {}

    virtual ~GaussPattersonExponentialGrowthRule() {}

    virtual value_type operator() (const value_type& x) const { 
      // Gauss-Patterson rules have precision 3*2*l-1, which is odd.
      // Since discrete orthogonality requires integrating polynomials of
      // order 2*p, setting p = 3*2*{l-1}-1 will yield the largest p such that
      // 2*p <= 3*2^l-1
      if (x == value_type(0)) return value_type(0);
      return 3*std::pow(value_type(2),x-value_type(1))-value_type(1);
    }

  };

}

#endif