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Wait, what? 2x slower than C is slow? And 2x performance gain is worth dropping from high to low-level programming? In what world, I'd like to ask? Do you frequently "just" write programs in asm to get additional performance gains?

It could well be that you really need every bit of performance; what I want to say is that areas where "2x slower than C" are few and far in between.

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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).

I really don't get debates like this. You should simply account for the (a) time it takes to write the program AND (b) the time it takes to run the program. Selecting a language only based on (b) is clearly suboptimal.

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