.. index:: EISFDiffSphere
This fitting function models the elastic incoherent intensity of a particle undergoing continuous diffusion but confined to a spherical volume [1], :ref:`EISFDiffSphere <func-EISFDiffSphere>`.
EISF(Q) = (3 \frac{j_1(QR)}{QR})^2(Q\cdot R)
R units are inverse of Q units. Because of the spherical symmetry of the problem, the structure factor is expressed in terms of the j_l(z) spherical Bessel functions.
Related functions: - :ref:`ElasticDiffSphere <func-ElasticDiffSphere>` - :ref:`InelasticDiffSphere <func-InelasticDiffSphere>` - :ref:`DiffSphere <func-DiffSphere>`
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Example - fit of Q-dependence:
.. testcode:: QdependenceFit q = [0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9] # A=2.0 and R=0.5 eisf = [1.9910173378712506, 1.9751335160492454, 1.9515113999365767, 1.9203919612905054, 1.8820909475511156, 1.8369942556092735, 1.7855523076069868, 1.7282735296640419, 1.6657170499144847] w = CreateWorkspace(q, eisf, NSpec=1) results = Fit('name=EISFDiffSphere', w, WorkspaceIndex=0) print(results.Function)
Output:
.. testoutput:: QdependenceFit name=EISFDiffSphere,A=2,R=0.5
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