Extending LatBuilder

Implementing Custom Weights

To compute weight values for any of the supported weight types (product, order-dependent, POD, projection-dependent), it is possible to use the enter an expression function from the web user interface. But let us assuming that we want to do this by deriving a new class of weights from an existing one. Consider product weights that depend a single parameter \(\eta\) and that take the value

\[ \gamma_{\mathfrak u} = \prod_{j \in \mathfrak u} (1 / j^\eta) \]

for projection \(\mathfrak u\). First, we define the new weights class that overrides ProductWeights::getWeightForCoordinate() in latticetester/include/latticetester/MyWeights.h:

#include "latticetester/ProductWeights.h"

namespace LatticeTester {

class MyWeights : public ProductWeights {
public:
   explicit MyWeights(Weight parameter=1.0) : m_parameter(parameter) {}
   virtual ~MyWeights() {} 
   virtual Weight getWeightForCoordinate(Coordinates::size_type coordinate) const
   { return std::pow(coordinate + 1, -m_parameter); }

protected:
   virtual void format(std::ostream& os) const
   { os << "MyWeights(" << m_parameter << ")"; }
   Weight m_parameter;
};

}

Next, we declare a new member function in Parser::Weights in include/latbuilder/Parser/Weights.h:

   static std::unique_ptr<LatticeTester::Weights>
   parseMyWeights(const std::string& arg, Real powerScale);

and implement it in src/Parser/Weights.cc:

std::unique_ptr<LatticeTester::Weights>
Weights::parseMyWeights(const std::string& arg, Real powerScale)
{
   auto ka = splitPair<std::string, Real>(arg, ':');
   if (ka.first != "my-weights") return nullptr;
   auto w = new LatticeTester::MyWeights(ka.second);
   return std::unique_ptr<LatticeTester::Weights>(w);
}

after, of course, adding the new header with:

#include "latticetester/MyWeights.h"

We also need to add a conditional block in Parser::Weights::parse:

   if (auto p = parseMyWeights(arg, powerScale))
      return p;

Then, after recompiling LatNet Builder, the new weights should be available to use by invoking latnetbuilder with the option –weights MyWeights:1.5, for example.