Re: [Boost-users] [math] finding c such that w1/c+...+wn/c < math::tools::max_value<T>()

21 Jul 2009


      ...
er wrote:
...
...
I'm now trying to generalize this i.e. find c such that w1/c+...+wn/c 
<=  C:
Finally, my solution below. Perhaps some room for improvement still?

     template<typename InIt>
     typename iterator_value<InIt>::type
     find_scale_finite_sum(
         InIt b,InIt e,
         typename iterator_value<InIt>::type low_init,
         typename iterator_value<InIt>::type high_init
         ){
         typedef typename iterator_value<InIt>::type val_;
         static val_ zero = static_cast<val_>(0);
         static val_ two = static_cast<val_>(2);
         static val_ eps = math::tools::epsilon<val_>();

         val_ low = low_init;
         val_ high = high_init;
         val_ mid = (low + high)/two;
         val_ delta, acc;

         do{
             delta = high - low;
             acc =
                 std::accumulate(b,e,zero, lambda::_1 + ( lambda::_2
/mid) );
             if(boost::math::isinf(acc)){
                 low = mid;
             }else{
                 high = mid;
             }
             mid = (low+high)/two;
         }while(
             delta - (high - low)>eps
         );
         return high;
     }


     // Overload finds initial low, high
     typename iterator_value<InIt>::type
     find_scale_finite_sum(
         InIt b,InIt e
     ){
	// Pseudo code:
	// i) Splits [b,e) into maximal size groups with
	// 	finite sums, [b1,e1)
	// ii) low = high =  find_scale_finite_sum(b1,e1,1,highest)
	// iii)  low/=2 and high*=2 until
	// 	isinf(sum), !isinf(sum), respectively
	// iv) return find_scale_finite_sum(b,e,1ow,high)

     }