C++ for Scientists - Technische Universität Dresden
C++ for Scientists - Technische Universität Dresden C++ for Scientists - Technische Universität Dresden
256 CHAPTER 12. REAL-WORLD PROGRAMMING By supplying the required parameters at construction time it is possible to homogenize the interface of the operator(). This methodology also allows the continued use of the old data structures in the initial phases of transition, while not being so constrictive as to hamper future developments. The functions for the state transitions are treated similarly to those for the rate calculation. Both are then fused in a scattering pack to form the complete scattering model and to ensure consistency of the rate and state transition calculations and which also models the runtime concept as can be seen in the following part of code: template struct scattering pack { // ... scattering rate type rate calculation; transition type state transition; scattering pack (const parameter type& parameters) : rate calculation(parameters), state transition(parameters) {} template numeric type rate(const StateType& state) const { return rate calculation(state); } template void transition(StateType& state) { state transition(state); } } The blend of runtime and compile time mechanisms allows the storage of all scattering models within a single container, e.g. std::vector, which can be iterated over in order to evaluate them. typedef std::vector scatter container type ; scatter container type scatter container ; scatter container.push back(scattering model) ; For the development of new collision models easy extendability, even without recompilations, is also a highly important issue. This approach allows the addition of scattering models at runtime and to expose an interface to an interpreted language such as, e.g., Python [?]. In case a highly optimized version is desired, the runtime container (here the std::vector) may be exchanged by a compile time container, which is also readily available from the GSSE and provides the compiler with further opportunities for optimizations at the expense of runtime adaptability.
12.1. TRANSCENDING LEGACY APPLICATIONS 257 12.1.2 Reuse Something Appropriate While the described approach initially slightly increases the burden of implementation, due to the fact, that wrappers need to be provided, it gives a transition path to integrate legacy codes into an up to date frame while at the same time not to abandoning the experience associated with it. The invested effort allows to raise the level of abstraction, which in turn allows to increase the benefits obtained from the advances in compiler technologies. This in turn inherently allows an optimization for several platforms without the need for massive human effort, which was needed in previous approaches. In this particular case, encapsulating the reliance on global variables of the functions implementing the scattering models to the wrapping structures, parallelization efforts are greatly facilitated, which are increasingly important with the continued increase of computing cores per CPU. Furthermore the results can easily be verified as code parts a gradually moved to newer implementations, the only stringent requirement being link compatibility with C ++. This test and verification can be taken a step further in case the original implementation is written in ANSI C, due to the high compatibility of it to C ++. It is possible to weave parts of the new implementation into the older code. Providing the opportunity to get very a fine grained comparison not only of final results, but of all the intermediates as well. Such swift verification of implementations allows to also speed up the steps necessary to verify calculated results with subsequent or contemporary experiments, which should not be neglected, in order to keep physical models and their numerical representations strongly rooted in reality.
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12.1. TRANSCENDING LEGACY APPLICATIONS 257<br />
12.1.2 Reuse Something Appropriate<br />
While the described approach initially slightly increases the burden of implementation, due<br />
to the fact, that wrappers need to be provided, it gives a transition path to integrate legacy<br />
codes into an up to date frame while at the same time not to abandoning the experience<br />
associated with it. The invested ef<strong>for</strong>t allows to raise the level of abstraction, which in turn<br />
allows to increase the benefits obtained from the advances in compiler technologies. This in<br />
turn inherently allows an optimization <strong>for</strong> several plat<strong>for</strong>ms without the need <strong>for</strong> massive human<br />
ef<strong>for</strong>t, which was needed in previous approaches.<br />
In this particular case, encapsulating the reliance on global variables of the functions implementing<br />
the scattering models to the wrapping structures, parallelization ef<strong>for</strong>ts are greatly<br />
facilitated, which are increasingly important with the continued increase of computing cores<br />
per CPU.<br />
Furthermore the results can easily be verified as code parts a gradually moved to newer implementations,<br />
the only stringent requirement being link compatibility with C ++. This test and<br />
verification can be taken a step further in case the original implementation is written in ANSI<br />
C, due to the high compatibility of it to C ++. It is possible to weave parts of the new implementation<br />
into the older code. Providing the opportunity to get very a fine grained comparison<br />
not only of final results, but of all the intermediates as well.<br />
Such swift verification of implementations allows to also speed up the steps necessary to verify<br />
calculated results with subsequent or contemporary experiments, which should not be neglected,<br />
in order to keep physical models and their numerical representations strongly rooted in reality.
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