Matrix inversion in Excel

Even the newest version of Excel has a limit on taking the inverse of a matrix. The maximum size is 52×52 (don’t ask me why this limit exists). What you get if you use minverse(your matrix) for a big matrix is this:

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Fortunately, there is a nice add-in programmed in C that does the trick. It was developed for Excel 2007 and earlier but it works fine in the newest version (2013).

You can download it from http://www.xcell.excelabo.net/english and it works like the inverse function in excel. Instead of minverse(….) you use minverse.ext(…).

PS. If you want to take the inverse of a matrix in excel, you mark the region, where the inverse should appear and then enter minverse(your matrix) and hit Ctrl-Shift-Enter (like for all array-operations in Excel).

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and after hitting Ctrl-Shift-Enter you get this:

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Getting rid of some annoyances when opening or saving in Excel 2013 (and Word, Access)

The new Office version (2013) has lots of new features, but also some annoyances. Especially saving and opening files need much more clicks.

If you want to open a file, Excel opens with a start screen. Disabling this one is easy: just go to File-Options-General Tab and disable “Show the Start Screen…”.

If you want to save a file, this is what appears in Excel

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Now you have to click on Browse to search the directory you want to save your files. It goes faster as follow, if you set the following options (see arrows) and set your favorite directory:

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Afterwards, it will look likes this if you want to save (Ctrl+S is the short-cut for that):

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Note, that if you use Ctrl-O for opening a file, you get the same results (instead of the “Backstage view”).

Managing papers with Org-Mode and Reftex

Writing papers means reading lots of papers, and I often lose track of all the papers I am reading: Where did I file a certain paper? Which paper did I start reading? Which paper might be interesting?

A reading list would be nice, but such a list should be easy to handle. I have all my papers catalogued in JabRef and use AucTex and RefTex for writing and Org-Mode for my tasks.The solution should therefore combine the strength of all three. I found a nice post on how to this (http://tincman.wordpress.com/2011/01/04/research-paper-management-with-emacs-org-mode-and-reftex/) and adopted it to my needs.

Here is how my solution looks like (for managing tasks with Org-Mode see one of my previous posts)

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  1. For every paper I am writing I have an org-file with my tasks, reading list, notes, and calls.
  2. I have four lists for my reading:
    1. Actual reading
    2. Should read: papers I glanced through and that look promising
    3. Not yet read: lower priority papers to be read
    4. Already read
  3. I insert new papers by using C-c ) (as in LaTeX/AucTex/RefTex). More on that later. Automatically, a link to this paper and the title are inserted (I save all papers as pdf-file and named with the first author name and the year of publication. They are all saved in the same dropbox directory). With “C-c C-c” I can tag the entries for easy searching later on.
  4. If I want to work on my paper, I open the org-file and, if I want to read a paper, I just click on its link and start reading.
  5. If necessary I can make short notes directly under the link.

Org-Mode makes it possible to use RefTex. For this it is necessary to put the information on where the bib-file is (third line in the next figure)

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The .emacs file has to be adjusted as follows:

Note: as I can make the reading to a TODO or a MIT (most important task), it will also show up in my daily agenda and I can also start reading from here by clicking on the link:

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