davidson() for ITensor

Question

Hi Miles,

Can I use davidson function to obtain the low-lying eigenvectors corresponding to a ITensor, and a given initial guess, similar to diagHermitian function? Is it possible to do?

Titas

EDIT

Motivated from the localmpo class, I have created a wrapper class for ITensor objects (in the matrix form, which is also required for diagHermitian), containing a const& of the actual object, say A. The wrapper class have three member functions -- (1) product(psi, phi) which computes A*psi and store it on phi; (2) diag() which returns diagonal tensor of A, can be easily defined using delta(); (3) size() which returns total dimension of all unprimed indices.

I hope, I am doing it correctly.

Answer 1

Hi Titas,
Yes that is exactly right. I'll make a note that we need to document the davidson function on the website to especially mention this information. (Before I had been thinking of it as a low level / internal function but it could indeed be useful for users such as yourself to take advantage of it.)

Thanks for the post which will be helpful to others wanting to implement this same thing.

Best regards,
Miles

Comments

Many thanks for the confirmation. There are lot of functions in the source, which are not on the documentation, but are really helpful. If you need any help to document those, please feel free to contact me.

Titas

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Hi Titas, that would be awesome if you wanted to help with documentation. If you do, then I will definitely credit you on the "About ITensor" page by listing your name and putting a badge labeling your contributions. (http://itensor.org/about.html)

The ITensor website is actually completely open source and is on Github: https://github.com/ITensor/website

So you can contribute to the documentation by forking that repo on Github, editing on your fork, then sending a pull request of your changes to us via Github.

Or if you want to just edit / create the relevant documentation file (following the pattern in this folder: https://github.com/ITensor/website/tree/master/docs/classes) then I can add it to the site for you.

Best regards,
Miles

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Sure... Thank you...