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## SAGE tip: rewriting expressions

Today I was calculating some stuff with the help of SAGE, and realize that the expressions got a lot (really, a lot) simpler if they where written in terms of  hyperbolic functions instead of exponentials.

$e^x = \cosh(x)+\sinh(x)$

$e^{-x} = \cosh(x)-\sinh(x)$

So I enter the sage-devel channel of IRC (freenode), but there was a lazy day around… Sunday. Therefore I decided to write to the sage-dev group on Google groups.

Francois Maltey answer my question on how to do the transformation… He has written a package that does it!

• Go to page http://wiki.sagemath.org/symbolics/rewrite
look at the second line the “attachement” (in smaller characters)
and get the most recent file.
• Then put this file in your Sage directory
In Sage, type : load “/the/good/file/in/the/good/directory’
Then call the rewrite function.
• Thank you Francois

#### Example

Suppose the path to the file is “/home/me/rewrite-xxx.sage”

```sage: load "/home/me/rewrite-xxx.sage" sage: A = exp(x) + exp(-x) sage: rewrite(A, 'exp2sinhconh') 2*cosh(x)```

If you go to http://wiki.sagemath.org/symbolics/rewrite, will find all possible commands which perform such transformations.

Enjoy!

Dox

## Mendeley: reference manager software

Since I download and read a lot of scientific papers (specially form arXiv and spires, or its recently upgraded environment, inspirebeta), oftenly I realice the way chosen for classify them is not the best… and the work starts almost from the beginning.

In Ubuntu there is a software called Referencer, which allows to manage you papers collection, but despite their advantages… I felt a bit discouraged (a.f.a.I.k. does not update automatically the list of papers in the folder).
You can try it,

`\$ sudo apt-get install referencer`

Looking for a substitute, I’ve found Mendeley.

http://www.mendeley.com/

You must Sign In for using it, and you could manage your references either on-line (you get 500M storage) or locally (after installing MendeleyDesktop).

### Installing Mendeley Desktop

Open the source.list file,

`\$ sudo nano /etc/apt/source.list`

`deb http://www.mendeley.com/repositories/xUbuntu_10.10 /`

Save the changes and exit.

#### Install the software

Update the repositories, and install

`\$ sudo apt-get update && sudo apt-get install mendeleydesktop`

### Running Mendeley Desktop

You can now run it by using the cli,

`\$ mendeleydesktop `

or by writing it after press Alt+F2.

If you have all your references in a folder, you can add them by clicking on File->Watch Folder and select the path to the folder you like.

The difference between adding a folder this way or just click on Add Folder, is that the former updates the data any time you re-open the application.

When documents are added to your library, Mendeley connects to internet data bases and try to get the right information about them… for documents from Spires and arXiv, the rate of success is high, but it fails getting data about Journal publication.

One can always add some data manually… hard way!!! 😛

At the upper-right corner there is a search bar, which allows you to narrow down through author, title, or even tag.

If you double-click on a paper it opens “inside” Mendeley, and the software allows you to highlight, add post-it to the PDF, copy text, and many other advantages.

<still un-finished>

## Controlling the Size of Emacs’ window

Some times, depending of the resolution of the monitor, the window of Emacs is bigger than it should. For controlling the size, I added a Lisp line to my .emacs file

`(setq default-frame-alist '((width . 80) (height . 33) (menu-bar-lines . 1)))`

which set the display to 80 columns and 33 rows.

Enjoy!

## Enabling Flyspell mode gave an error

After upgrade to Ubuntu 10.10, my emacs got a bug. Whenever I wanted to enable the flyspell-mode, minibuffer answer was “Enabling Flyspell mode gave an error”, no more information were given even with the debugger turned on.

Some googling, web surfing, et cetera… and still nothing.

Finally, right now (after almost 3 week, and quasi-given up), it occurs to me that and update of Emacs could solve the problem… How?

THAT’S IT!!!!! I looked for an Emacs PPA source,

```\$ sudo add-apt-repository ppa:ubuntu-elisp/ppa \$ sudo apt-get update \$ sudo apt-get dist-upgrade```

And problem solved.