# Changeset 4476951 in sasmodels

Ignore:
Timestamp:
Jun 28, 2018 9:09:47 AM (4 years ago)
Branches:
master, core_shell_microgels, magnetic_model, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests
Children:
3b8a004
Parents:
5c36bf1
Message:

applied fix for ticket 1112 (allow negative rg)

File:
1 edited

### Legend:

Unmodified
 r2d81cfe .. math:: I(q) = \text{scale} \cdot \exp{\left[ \frac{-Q^2R_g^2}{3} \right]} I(q) = \text{scale} \cdot \exp{\left[ \frac{-Q^2 R_g^2 }{3} \right]} + \text{background} .. math:: q = \sqrt{q_x^2 + q_y^2} Note that $R_g^2$ may be negative, which happens when a form factor $P(Q)$ is increasing with $Q$ rather than decreasing. This can occur for core or shell particles, hollow particles, or for composite particles with domains of different SLDs in a solvent with an SLD close to the average match point. (Alternatively, it might be regarded as there being an internal inter-domain "structure factor" within a single particle which gives rise to a peak in the scattering). To specify a negative value of $R_g^2$ in SasView, simply give $R_g$ a negative value ($R_g^2$ will be evaluated as $R_g |R_g|$). Note that the physical radius of gyration, of the exterior of the particle, will still be large and positive. It is only the apparent size from the small $Q$ data that will give a small or negative value of $R_g^2$. References #             ["name", "units", default, [lower, upper], "type","description"], parameters = [["rg", "Ang", 60.0, [0, inf], "", "Radius of Gyration"]] parameters = [["rg", "Ang", 60.0, [-inf, inf], "", "Radius of Gyration"]] Iq = """ double exponent = rg*rg*q*q/3.0; double exponent = abs(rg)*rg*q*q/3.0; double value = exp(-exponent); return value;