Re: [Gretl-users] precision / format of large (integer) numbers imported in gretl
Am 04.01.2018 um 11:13 schrieb Schaff, Frederik:
Happy New Year!
And to you! (and everybody)
guess it is a problem with large integer (part) of the numbers? Is
this
only the visible behaviour or can it really distort the data and
computations? In this case it wouldn’t matter, but in other cases it might…
There are two separate issues here, the internal number representation
and the printed format.
AFAIK in gretl basically everything is stored as a double precision
float (should be 64 bit == 8 byte wide). It is a standard computer
science thing that floating point numbers cannot exactly represent all
integers, and in principle you also have the possibility of overflow. In
this (very old and universal) sense yes in principle it could affect the
results. This is not usually a problem in practice, however.
The limited number of digits/precision which is displayed is different
from that. There are some 'set' options for that for example, quoted
from the command ref:
<doc>
- display_digits: an integer from 3 to 6, specifying the number of
significant digits to use when displaying regression coefficients and
standard errors (the default being 6). This setting can also be used to
limit the number of digits shown by the summary command; in this case
the default (and also the maximum) is 5, or 4 when the --simple option
is given.
- mwrite_g: on or off (the default). When writing a matrix to file as
text, gretl by default uses scientific notation with 18-digit precision,
hence ensuring that the stored values are a faithful representation of
the numbers in memory. When writing primary data with no more than 6
digits of precision it may be preferable to use %g format for a more
compact and human-readable file; you can make this switch via set
mwrite_g on.
</doc>
In the "show values" (zeige Werte) window there is also a button number
format (Zahlenformat) where a different display can be chosen.
hth,
sven