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Which variables are automagically defined in the sage shell?

asked 2013-01-03 01:21:01 -0600

Thomas gravatar image

I'm using the sage-5.5 command line and some variables are automatically declared. For instance I can do

f = x^2

but not

f = t^2

My question: How does this come about? Which variables are defined like this? Where is this documented?

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answered 2013-01-03 01:47:58 -0600

kcrisman gravatar image

See sage/all.py and sage/all_cmdline.py in the devel/sage directory. In addition to x, we define oo to be infinity, e to be the base of the natural log, i to be a certain root of $x^2-1=0$, ZZ to be the integers, and some other things - and of course lots and lots of functions.

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You could also do `globals()` to find everything at all, but I don't think that is what you meant.

kcrisman gravatar imagekcrisman ( 2013-01-03 01:49:09 -0600 )edit

Interesting effect: Type "globals()" in a session where you have done 'a few' plots before.

Thomas gravatar imageThomas ( 2013-01-03 02:37:50 -0600 )edit
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First I was not convinced since in sage/all.py the line defining x is commented out (both, in your linked version and in the file on my disk), but then I saw that it comes from the line "from sage.calculus.predefined import x" in all_cmdline.py. Thanks.

Thomas gravatar imageThomas ( 2013-01-03 02:42:17 -0600 )edit

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Asked: 2013-01-03 01:21:01 -0600

Seen: 81 times

Last updated: Jan 03 '13