Failure of default_format_1.f90

[Dominique Dhumieres]

> The default widths for list-directed output should be
> consistent with PRECISION().

The relative accuracy of FP is not constant: it doubles over the interval
[1.0,2.0[ + a worse effect in decimal representation. PRECISION() is just
the integer lower bound of the worst case.

In practical applications, the actual "numerical" accuracy is below
PRECISION(). For my typical applications ~13 digits for stable cases,
going to 5/6 near the instability thresholds (based on the number of stable 
digits when changing optimization/platform).

Dominique