[superkelle]

Hi my problem is that in my simulations some numeric values are very small, in regions of 1E-40 for example a approximation for a rate coefficient field :

k4.field() = 1.5E-40*pow(TGas.field()/300, -2.5);

all values are simply set to zero. Is there a setting to prevent this? Or is it simply to small in terms of machine epsilon?

[HPE]

Have a look at the machine epsilon table below, and compare it with your hardware:
Machine epsilon

[superkelle]

from python I got:

import sys
sys.float_info.epsilon

Out[2]: 2.220446049250313e-16

So does that really mean that if I am making calculations in OF, I will not get right (adequate) results in any equation, when I have any value involved that is in this region or lower? I found out that it was maybe a limit of paraview in the first place to display small values, since when I multiplied this value with some big values in the region of 1E40 the results were not zero.

[HPE]

yes, those numbers lower than the machepsilon ks mumbo jumbo most of the time to avoid fp exceptions.

[superkelle]

Hi for everyone who sees this post, here is a complete discussion about the topic.

is double precision default of OF?

in short:

Be aware that you can work with numbers much smaller than eps, as the maximum and minimum exponents (with 10-base) is -308 and 308 respectively (double prec.). That means that it is possible to represent a number down to to 2.2250738585072014e-308 (equal to 2^-1022) in double precision. It is also perfectly possible to do arithmetics with small numbers, for example 1e-30 + 1e-30 equals (correctly) 2e-30. The trouble arise when the numbers differ greatly in magnitude. If you for example try to calculate the sum 1+10^-16, the result is still 1 (exactly).

See this page for more information: http://en.wikipedia.org/wiki/Double-...g-point_format