Documentation error for lamellar_stack_paracrystal model

[jfmoulin]

Describe the bug
Equation 4 of the doc page for the paracrystal lamellar model is incorrect:

S_N(q) = \frac{a_N}{N}[1 + w^2 - 2 w \cos(q \langle D \rangle)]^2

should instead read:

S_N(q) = \frac{a_N}{N [1 + w^2 - 2 w \cos(q \langle D \rangle)]^2}

The c code computing the model correctly implements the second form of the equation.

SasView version (please complete the following information):

• Version: 6.0

Operating system (please complete the following information):

• Linux

[smk78]

Many thanks for bringing this to our attention.

[smk78]

Does this need transferring to sasmodels?

[bmaranville]

Seems to be the same wrong formula in 22 different places, in 3 different repos:

sasmodels repo:

• sasmodels/models/lamellar_stack_paracrystal.py

sasfit-models repo:

• sasmodels/models/lamellar_stack_paracrystal.py

docs repo:

• _sources/user/models/lamellar_stack_paracrystal.rst.txt
• old_docs/5.0.5/user/models/lamellar_stack_paracrystal.html
• ... a bunch more

[bmaranville]

https://github.com/search?q=org%3ASasView+S_N%28q%29+%3D+%5Cfrac%7Ba_N%7D%7BN%7D&type=code&p=2

[smk78]

Thanks @bmaranville . I'm of the opinion we shouldn't retrospectively change the documentation for previous versions. I'm sure there are many of uncaught typos like this. But we should push a fix that will feed into the next point release of SasView.

[pkienzle]

Does this need transferring to sasmodels?

Yes