Programming Languages

Among the decades, very many programming languages has been evolved. We list some most widely used in the context of HPC here.

Low-Level programming languages

• Machine code: That are 10001001011110 your computer can understand. You likely not.
• Assembler: human-readable (to somehow extent; many says 'for special humans'), but still very low-level. Allows the programmer to get the very last possible performance crumbs from the hardware, but in turn is hardware-dependent and very tedious to program. Highly-tuned libraries often contain ASM parts, often making this software less-portable. You should not start at assembler level when programming an application.

High-level programming languages

... are readable by humans. The source code is a text file, to be translated to an executable file by a compiler (we do not want to introduce the definition bush about compiled and interpreted languages here). In addition to human-readablity these programs are portable, you just need to recompile your code on another hardware using a compiler understanding the same language. Note that being standard-compliant for both the code and the compiler greatly enhance the chances of porting to be a smooth, enjoyable procedure.

• Fortran, the 1st wide-used high-level programming, used in HPC since 1954 and will likely be used for a long time, as there are still many Fortran projects and tons of libraries-canot-give-up around. Fortran handles multi-dimensional arrays very comfortably. Due to some restrictions in the memory handling the compiler has more optimisation freedom leading to quite well-performing code out of the box, usually.

• C and C++ are related languages with the second being object-oriented, with a lot of programming comfort. “C programs are the fastest” is usually not true. As C has very few syntax limitations, this often gives the compiler a hard time optimizing. The passing of pointers is in most cases the biggest handicap. You can rid this, but need to take care.

• JAVA is a widely used programming language, but due to performance issues in most cases not suited for true high performance computing.

Script / interpreted languages

• Shell helps you to script many calls to a single program. The batch scripts are programmed in one of Shell languages.
• Python evolves to very powerful scientific computing language nowadays, especially for those prepared to abadon MATLAB from the compute pipeline.
• Perl is another scripting language with very powerful handling of regular expressions.
• MATLAB is a powerful numerical computing environment with same-called programming language.

References

tbd.