UserExpression

Source: tests/expression/UserExpression.cpp

// ========================================================================= //
// This file is part of MyraMath, copyright (c) 2014-2019 by Ryan A Chilton  //
// and distributed by MyraCore, LLC. See LICENSE.txt for license terms.      //
// ========================================================================= //

#include <myramath/expression/Expression.h>
#include <myramath/expression/UserExpression.h>
#include <myramath/expression/Index.h>

#include <myramath/expression/print.h>

// Reporting.
#include <tests/myratest.h>

using namespace myra;

class PascalExpression
  {
  public:

    // Required typedefs/constants.
    const static int Arity=2;
    typedef double Number;

    // Constructor, requires size info.
    PascalExpression(int in_N)
      : N(in_N) { }

    // Size inspector.
    Index<Arity> size() const
      { return make_Index(N,N); }

    // Evaluate method.
    double evaluate(Index<Arity> ij) const
      {
      int i = ij[0];
      int j = ij[1];
      return choose(i+j,i);
      }

  private:

     // Implementation detail of evaluate()
     static double choose(int n, int k)
       {
       double answer = 1.0;
       for (int i = 1; i <= k; ++i)
         {
         answer *= static_cast<double>(n-k+i);
         answer /= static_cast<double>(i);
         }
       return answer;
       }

     // Size, a Pascal matrix is always square.
     int N;
  
  };

ADD_TEST("UserExpression","[expression]")
  {
  auto E = make_UserExpression( PascalExpression(10) );
  myra::out() << E << std::endl;
  // TODO compute/interrogate the Cholesky triangle of E, it's very structured.
  }

Results: [PASS]

size 10 by 10 arity-2 Expression of double: 
[ 1 1 1 1 1 1 1 1 1 1 ]
[ 1 2 3 4 5 6 7 8 9 10 ]
[ 1 3 6 10 15 21 28 36 45 55 ]
[ 1 4 10 20 35 56 84 120 165 220 ]
[ 1 5 15 35 70 126 210 330 495 715 ]
[ 1 6 21 56 126 252 462 792 1287 2002 ]
[ 1 7 28 84 210 462 924 1716 3003 5005 ]
[ 1 8 36 120 330 792 1716 3432 6435 11440 ]
[ 1 9 45 165 495 1287 3003 6435 12870 24310 ]
[ 1 10 55 220 715 2002 5005 11440 24310 48620 ]

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