Changeset 4476951 in sasmodels
 Timestamp:
 Jun 28, 2018 9:09:47 AM (4 years ago)
 Branches:
 master, core_shell_microgels, magnetic_model, ticket1257vesicleproduct, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests
 Children:
 3b8a004
 Parents:
 5c36bf1
 File:

 1 edited
Legend:
 Unmodified
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 Removed

sasmodels/models/guinier.py
r2d81cfe r4476951 7 7 .. math:: 8 8 9 I(q) = \text{scale} \cdot \exp{\left[ \frac{Q^2 R_g^2}{3} \right]}9 I(q) = \text{scale} \cdot \exp{\left[ \frac{Q^2 R_g^2 }{3} \right]} 10 10 + \text{background} 11 11 … … 19 19 20 20 .. math:: q = \sqrt{q_x^2 + q_y^2} 21 22 Note that $R_g^2$ may be negative, which happens when a form factor $P(Q)$ is 23 increasing with $Q$ rather than decreasing. This can occur for core or shell 24 particles, hollow particles, or for composite particles with domains of 25 different SLDs in a solvent with an SLD close to the average match point. 26 (Alternatively, it might be regarded as there being an internal interdomain 27 "structure factor" within a single particle which gives rise to a peak in the 28 scattering). 29 30 To specify a negative value of $R_g^2$ in SasView, simply give $R_g$ a negative 31 value ($R_g^2$ will be evaluated as $R_g R_g$). 32 33 Note that the physical radius of gyration, of the exterior of the particle, 34 will still be large and positive. It is only the apparent size from the small 35 $Q$ data that will give a small or negative value of $R_g^2$. 21 36 22 37 References … … 42 57 43 58 # ["name", "units", default, [lower, upper], "type","description"], 44 parameters = [["rg", "Ang", 60.0, [ 0, inf], "", "Radius of Gyration"]]59 parameters = [["rg", "Ang", 60.0, [inf, inf], "", "Radius of Gyration"]] 45 60 46 61 Iq = """ 47 double exponent = rg*rg*q*q/3.0;62 double exponent = abs(rg)*rg*q*q/3.0; 48 63 double value = exp(exponent); 49 64 return value;
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