HP Fortran Programmer's Guide (March 2010)

Performance and optimization
Vectorization
Chapter 6176
Fortran uses implicit typing by default. Unless a function is explicitly declared as having a
certain type, the type is determined by the first character of the BLAS routine. If that
character implies a type other than that of the returned value, the result will be meaningless.
See the HP Fortran Programmer's Reference for information about the BLAS library.