Phase Space Volume

[jiangyi15]

Function phsp_volume to calculate the Volume of phase space

$$ \int 1 d\Phi = \frac{1}{2(2\pi)^{2n-3}M} \int |p{1}| \prod{i=1}^{n-2}|p_{i+1}^{*}| d M_i $$

from tf_pwa.phasespace import phsp_volume

value = phsp_volume(3.0, [0.1, 0.2, 0.3])
value, error = phsp_volume(3.0, [0.1, 0.2, 0.3], N=10000, return_error=True)

For decay $a\rightarrow b + c$,

$$ q = \frac{\sqrt{(m_a^2-(m_b+m_c)^2)(m_a^2-(m_b-m_c)^2)}}{2m_a} $$

is used.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.44444% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 78.31%. Comparing base (42f0ac0) to head (c18318d).

Files	Patch %	Lines
tf_pwa/phasespace.py	94.44%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #143 +/- ## ========================================== + Coverage 78.28% 78.31% +0.03% ========================================== Files 121 121 Lines 18178 18214 +36 Branches 3407 3414 +7 ========================================== + Hits 14230 14264 +34 - Misses 3198 3199 +1 - Partials 750 751 +1 ``` | [Flag](https://app.codecov.io/gh/jiangyi15/tf-pwa/pull/143/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jiang+Yi+%28%E8%92%8B%E8%89%BA%29) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/jiangyi15/tf-pwa/pull/143/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jiang+Yi+%28%E8%92%8B%E8%89%BA%29) | `78.31% <94.44%> (+0.03%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jiang+Yi+%28%E8%92%8B%E8%89%BA%29#carryforward-flags-in-the-pull-request-comment) to find out more.

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