Dev/keldysh dlr new imaginary time Green's function type with DLR representation using Lehmann.jl

[HugoStrand]

Dear Igor,

This is pull request that adds a new imaginary time Green's function type using the Discrete Lehmann Representation and Lehmann.jl. This enable us to represent hybridization functions at a desired accuracy using very few coefficients, and enabling arbitrary interpolation by evaluating a few exponential functions.

The feature is "opt in" in the sense that the user can construct hybridization functions of DLRImaginaryTimeGF type instead of the standard equidistant ImaginaryTimeGF and pass them on to QInchworm.jl.

[krivenko]

Hey Hugo,

A quick question before I do a proper review. Do you insist on using your own DOS integration routine (semi_circular_g_tau()) in test/keldysh_dlr.jl instead of Keldysh.dos2gf()?

[HugoStrand]

Dear Igor, No I do not insist. Please let me have a go at removing that (and the QuadGK dependence). Thank you for asking.

[krivenko]

Please let me have a go at removing that (and the QuadGK dependence).

No need to. I have already removed it but wanted to ask you before commiting.

[krivenko]

I generally try to follow the Blue Style Guide for Julia. Let us stick to the 92 character line length limit it recommends.

[HugoStrand]

Dear Igor,

Thank you for the 2nd round of feedback. For some reason I can not reply directly under some of your comments. I have adopted all your suggestions and added tests for same statistics in the Green's function arithmetic operations involving two Green's functions.

Please have a look when you are back from vacation.

Cheers, Hugo

[krivenko]

Hey Hugo,

For some reason I can not reply directly under some of your comments.

This might have something to do with those comments being non-review comments...

Please have a look when you are back from vacation.

I'd say this PR is ready to be merged today provided you resolve the last remaining issue: #8 (comment)

[HugoStrand]

As per in person discussion I am merging this. Thank you for the help @krivenko!