[SasView Users] Bug Report – Unexpected Behavior of Polydispersity in SASview v6

[Stephen King - STFC UKRI via users]

Dear Fatemeh,

Thank you for your report.

I just tried your steps to reproduce with one of our example datasets using SasView 6.1.0, and 6.1.1 we released last week.

I don't see any behaviour that immediately leaps out at me as 'unrealistic'. So I'd like to understand exactly what you mean by this.

Could you post a few slides with annotated screenshots illustrating what you have done/see, please?

By the way, you posted to users at sasview.org which goes to a wider audience than just the developers. If you are comfortable with that, that's cool. Otherwise reply to help at sasview.org.


Kind regards,
Steve King

On behalf of the SasView Developer Community
________________________________
From: users <users-bounces at lists.sasview.org> on behalf of Abdoltajedini, Fatemeh via users <users at lists.sasview.org>
Sent: 08 October 2025 21:21
To: users at sasview.org <users at sasview.org>
Subject: [SasView Users] Bug Report – Unexpected Behavior of Polydispersity in SASview v6

Dear SASview Team,
I would like to report a possible bug I encountered in SASview v6 related to polydispersity.
Description of the issue:
When I add polydispersity to a model, the scattering curve changes far more dramatically than expected. Even small values (e.g., 0.05 on radius) cause the intensity and curve shape to shift disproportionately, which does not seem physically reasonable.
Steps to reproduce:

  1.
Open SASview v6.
  2.
Load the [Core-Shell Cylinder].
  3.
Fit the model without polydispersity – the curve looks reasonable.
  4.
Add a small polydispersity (e.g., 0.05 on radius).
  5.
The curve changes strongly in both shape and magnitude.

Expected behavior:
Polydispersity should broaden or smooth features of the scattering curve, but not cause large intensity changes or unrealistic distortions.
Observed behavior:
Even small polydispersity values produce a strong, unrealistic effect.
Environment:

  *
SASview version: 6.x

  *
Operating system: Windows
  *
Data used: experimental data

Thank you for your help and for maintaining this valuable software.
Best regards,
Fatemeh


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