The c_v coherence measure was proposed and described in a systematic framework of coherence measures by Röder et al.
The best performing coherence measure [...] is a new combination found
by systematic study of the configuration space of coherence measures.
This measure (CV) combines the indirect cosine measure with the NPMI
and the boolean sliding window. This combination has been overlooked
so far in the literature.
I recommend to read the original paper to understand the different steps (segmentation, probability calculation, confirmation measure and aggregation) behind this measure and others, such as u_mass, c_uci or c_npmi, as well. The authors use a consistent notation to describe all coherence measures in a systematic framework. You will find the formulas in the paper.
⚠️ However, there are a couple of issues with this coherence measure.
Therefore, the authors don't recommend to use it anymore.
It's not recommended to use CV because there are known issues associated with it.
Röder, M., Both, A., & Hinneburg, A. (2015). Exploring the space of topic coherence measures. WSDM 2015 - Proceedings of the 8th ACM International Conference on Web Search and Data Mining, 399–408. https://doi.org/10.1145/2684822.2685324