**PARI/GP**

During this REU we will work though a bunch of algebraic geometry. While we do so we will write computer algebra scripts that “verify” the mathematics is correct. The goal is not to write good/fast code. Rather we use writing and running a working script as a sort of verification that we understood what is going on completely. Johan will explain the reasoning behind this in the first meeting.

We will use the scripting language GP to do this. Here are some of the reasons for using this language and not an other:

- Johan is quite familiar with it (and not with any other mathematical packages)
- It is completely free
- Nobody knows this language so you should all be at the same disadvantage
- The scripts are (usually) very easy to read and we can share them between us

PARI/GP is not a computer algebra package, rather it is a number theory package. This means that it doesn't come with stuff like Groebner basis packages, etc. I actually think this is good for us, so we can't use advanced stuff without understanding what we are doing. Moreover, we can roll our own: we can eventually write a little bit more code doing more complicated things if it turns out we need it (it always turns out in practice that a better algorithm is worth more than better code).

Suggested work flow for each of you:

- Download PARI/GP and install on the computer you will work with
- Working on a script, write it in a text editor
- Whenever you do a run load it into the PARI/GP interpreter using \r
- Whenever you take a break from working upload your script to your upload page as a way to save it. (I think I may need to improve permissions for you guys so you can replace older scripts with newer ones???)

**PARI/GP on a MAC**

There are several ways to install it on a Mac:

- Download the source and compile it yourself. I strongly suggest you do
**not**do this unless: you already have XCODE (from apple) installed on your mac and you know what compiling a software package means in practice. - Install fink and install the pari/gp package from it.
- Install macports and install the pari/gp package from it. Fink seems to be preferred over macports by the pari/gp people…
- Install the binary version of sage for mac os and use the gp that comes with it. You can access it, once sage is installed, by something like /path/to/sage -gp. (There is a “install_scripts” command inside of sage that will get you a stand alone gp… Try running it with a question mark first, like so “install_scripts?”.) Johan has in the past installed sage on his computer with good results (and it is easily uninstalled).

Good luck!

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