Fortran was meant to be a high-level language at the time, so chose 1-based indexing. When C and lower-level languages came on the scene they reverted it back to zero-based, since this is more appropriate at the lower hardware level. CBLAS is zero-based.<p>Intel&#x27;s Math Kernel Library, which is a performant math library hand-tuned for Intel processors is zero-based in MKL-CBLAS.<p>It all depends on what you are familiar with, and staying consistent in use. I just use zero-based indexing in J and C and my numerical low-level work.