IF (logical_expr) IF(arith_expr)n1, n2, n3 in ODEPACK

1

File www.netlib.org/odepack/opkda2.f contains old versions of some BLAS routines. In it, we can see three instances of a disallowed IF (logical_expression) executable_statement:

S:\LANG>grep -in " if .* if " opkda2.f
630:      IF (INCX .EQ. INCY) IF (INCX-1) 5,20,60
719:      IF (INCX .EQ. INCY) IF (INCX-1) 5,20,60
812:      IF (INCX .EQ. INCY) IF (INCX-1) 5,20,60

According to the Fortran 66 standard, section 7.1.2.3, the executable statement S in
IF (e) S is not allowed to be itself an IF statement or a DO statement. Yet current compilers accept the disallowed combination, unless a compiler flag causes the arithmetic IF to be flagged as obsolescent.

Why is the statement accepted, can anyone tell? Thanks.

2

Not quite. It states that it may not be another logical IF statement, but here you have an arithmetic IF statement, which is allowed.

HTH

Mike

2 Likes
3

Ah, I see! Thanks.