Comment by adrian_b

In the past, Fortran was always faster than C in scientific computation applications, mainly because many optimizations are prevented when compiling C, by the risk of pointer aliasing.

In modern C, such optimizations are possible by using "restrict".

Nevertheless, few C programmers bother to write "restrict" wherever it should be used, so casually written C code remains slower than similarly written Fortran code.

Moreover, modern Fortran has a lot of builtin operations for multidimensional arrays, which can be implemented in an optimized way by the compiler.

Writing simple C code cannot achieve a comparable effect.

Achieving a similar performance in C would require a special optimized library and this would result in extremely verbose and ugly C code. It is really impractical to do this in C and C++ must be used, with operator overloading, iterators and templates being needed to write a custom library that can match or exceed the builtin features of Fortran.