Numerical calculations (e.g. DMRG) on large systems easily take days, if not weeks, to converge sensibly. At the same time, the algorithms can be implemented in

Numerical calculations (e.g. DMRG) on large systems easily take days, if not weeks, to converge sensibly. At the same time, the algorithms can be implemented in a relatively small amount of code (500 sloc in the Python prototype with some help from Numpy and Scipy, about 10k in C++). So, yes, if code can be reused later on and spending a month rather than a week writing it will save you many thousand hours of CPU time, it might well make sense not to use some high-level language (although I wouldn’t classify C++11 as low-level, albeit sometimes a bit verbose).