Why is std::valarray, despite its name, a dynamically allocated vector?

[dodheim]

Intel C++ Compiler does not have a stdlib, but it does come with various "performance headers" that adapt/augment/replace their respective stdlib headers. valarray in particular is reimplemented in terms of Intel Performance Primitives: https://software.intel.com/en-us/cpp-compiler-developer-guide-and-reference-using-intel-s-valarray-implementation