Triangular vertex support

[katanin]

Summary

Including triangular vertex support and respective corrections for the finite frequency box seems desirable.

Motivation

These vertices are in fact closely related to 4-point vertices and susceptibilities.

Implementation

It seems that they can be included also.

Formatting

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[katanin]

No support of triangular vertex calculation (1 bosonic + 2 fermionic) and their relation to 4-point vertices and susceptibilities. This includes both, full triangular vertex, as well as its U-irreducible part. Corrections to finite frequency box can be also absorbed there (see, e.g., Phys. Rev. B 101, 035110 (2020) and Appendix A of Phys. Rev. B 104, 245142 (2021)), which make calculation with finite frequency box more reliable.

[HugoStrand]

Dear Andrey,

Thank you for reaching out. We have basic support for "triangular" two frequency objects, see
https://triqs.github.io/tprf/latest/user_guide/dmft_susceptibility_dbse/dmft_susceptibility_dbse.html

Please note that TPRF is an open source community effort. If there is some functionality you need, you are very welcome to implement it and contribute your implementation to TPRF.

Please send my regards to Ivan.

Best regards,
Hugo