Corrected cylinder docs

[butlerpd]

Corrected equation one by removing the incorrect $\sin\alpha$ term in equation one. Also replaced P(q) with I(q) which is more correct in this case and eventually should be normalized across all models. Also updated the "last modified by" tag

[pkienzle]

You may want to move the u-substitution comment down. That is,

P(q) = F²(q) =∫₀^π/2 F²(q, α) sin α dα

and so

I(q) = scale/V ∫₀^π/2 F²(q, α) sin α dα + background

After substitution with u = cos α, du = sin α dα,

P(q) = ∫₀¹ F²(q, u) du
I(q) = scale/V ∫₀¹ F²(q, u) du + background

[yunliu01]

The proposed changes are reasonable to me.
However, I feel that it may be useful to make some additional changes to the following line:
P(q)=F^2(q)=\int_{0}^{\pi/2}{F^2(q,\alpha)\sin(\alpha)d\alpha}=\int_{0}^{1}{F^2(q,u)du}

It may be better to change it to
P(q)=F^2(q)=\int_{0}^{\pi/2}{F^2(q,\alpha)\sin(\alpha)d\alpha}

The concern is that F^2(q, u) may confuse people.
We already used F^2(q,\alpha) as the form factor.
When using F^2(q, u), we implied that u = \alpha. However, in fact, u = cos(\alpha).

[pkienzle]

Looking at the code, the cylinder model does not use a u-substitution for the integral. It could, and similar functions do, but it does not.