Opened 8 years ago
Last modified 8 years ago
#562 new defect
fix handling of q==0 for various models
Reported by: | pkienzle | Owned by: | |
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Priority: | minor | Milestone: | SasView Next Release +1 |
Component: | SasView | Keywords: | |
Cc: | Work Package: | SasView Bug Fixing |
Description
A number of models do not return a finite value at q = 0.
adsorbed_layer → inf
binary_hard_sphere → nan
broad_peak → inf
correlation_length → inf
fractal → nan
linear_pearls → nan
mass_fractal → nan
polymer_excl_volume → nan
porod → inf
power_law → inf
star_polymer → nan
surface_fractal → nan
two_power_law → inf
The -zero option to compare will cause q=0 to be included in the set of q to be calculated. You may want to add a test against a specific value for q=0, but this is optional; once these models are fixed we can include a check for finite q=0 as part of model_test.
Change History (3)
comment:1 Changed 8 years ago by pkienzle
comment:2 Changed 8 years ago by butler
Note that this becomes a problem when smearing with broad resolution function at low Q (i.e. do you have to include I(q=0) or close enough to zero for single precision for example to diverge?
NOTE: the discussion about USANS smearing being more problematic because of its very large q spread is not in fact a particular issue here since one is smearing over qy=0 but qx is definitely well outside of zero hence q=(qx^{2}+qy^{2})^{0.5} is not in fact ever zero.
It can however be a problem when simulating (a theory curve) in 2D without a beamstop. SasView may currently allow that so would need to be checked.
comment:3 Changed 8 years ago by pkienzle
- Milestone changed from SasView 4.0.0 to SasView Next Release +1
Some models do go to infinity at q=0 (power law, porod, fractals?); these can include explicit tests for infinity at zero.
Still need special handling in the code to suppress the divide by zero warning:
or avoid the divide by zero: