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Hidden features of Sage

asked 2013-04-28 18:09:50 -0500

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In the spirit of the StackOverflow threads of "hidden" language features, we can use this thread (community wiki) to aggregate useful but little-known features or tricks of Sage. Perhaps these can be collected and added to the documentation in the future.

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answered 2013-04-28 18:11:50 -0500

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Symbolic variables can be created from the command line as follows, faster than typing out var('x y z'):

,var x y z
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10

answered 2013-04-28 18:17:51 -0500

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In the command line, the underscore is a variable holding the result of the last output. This is very useful, e.g., for the following:

sage: integrate(cos(x), x)
sin(x)
sage: diff(_, x)
cos(x)
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answered 2013-04-28 18:48:17 -0500

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To preview LaTeX code from the command line, use the following:

show(LatexExpr(r'\frac{3}{4}x + 3'))

From the notebook,

html(r'$\frac{3}{4}x + 3$')

also works.

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Comments

1

By the way, it would be useful (if it doesn't already exist) to have a function to render LaTeX code to an image just large enough to fit the expression, for export to environments that do not support LaTeX (an HTML website, for example).

Eviatar Bach gravatar imageEviatar Bach ( 2013-04-28 19:06:38 -0500 )edit
0

answered 2013-04-28 18:49:56 -0500

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Sébastien Labbé has a blog post with various Sage tricks.

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1

answered 2013-04-28 22:13:24 -0500

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Though is general for python, it is always worth reading: Code like a Pythonista

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5

answered 2013-05-16 01:31:06 -0500

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The preparser() function which allows to understand differences between Python and Sage parsers, and between .py and .sage files:

sage: 2^2   
4
sage: preparser(False)
sage: 2^2
0
sage: 2**2
4

Conversely, the preparse() function tells you how Sage preparses the input:

sage: preparse('1.0+2^2')     
"RealNumber('1.0')+Integer(2)**Integer(2)"
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8

answered 2013-05-16 01:32:41 -0500

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The import_statements() function, which allows to know what import statement should we do to use an object.

sage: import_statements('RDF')
from sage.rings.real_double import RDF
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By the way, it would be http://www.faqtory.co/sky/ (useful) (if it doesn't already exist) to have a function to render LaTeX code to an image just large enough to fit the expression

mariakatosvich gravatar imagemariakatosvich ( 2016-09-12 04:11:43 -0500 )edit
3

answered 2013-05-16 03:00:10 -0500

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To know whether Sage is running from the notebook or the command line, use the misc.embedded() function:

sage: misc.embedded()
False
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3

answered 2013-05-20 09:25:42 -0500

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Locally disable the preparser with the suffix r

It's not really disabling the preparser (the input is still preparsed), but telling the preparser not to process some of the (numerical) input by marking this input as raw (by appending the letter r).

sage: type(12)
<type 'sage.rings.integer.Integer'>
sage: type(12r)
<type 'int'>

sage: type(42.42) 
<type 'sage.rings.real_mpfr.RealLiteral'>
sage: type(42.42r)
<type 'float'>

Also works for Python complex numbers:

sage: type(1j)
<type 'sage.rings.complex_number.ComplexNumber'>
sage: type(1jr)
<type 'complex'>

It's a bit similar to specifying some strings as raw by prepending an r to '...' or "..." or '''...''' or """..."""; for instance in '\t' the backslash-t produces a tab, but in r'\t' it stays backslash-t.

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5

answered 2013-05-28 09:24:02 -0500

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It is possible to delete user-defined variables, and reset Sage variables back to their default:

sage: a = 1 ; a
1
sage: reset()
sage: a
NameError: name 'a' is not defined

It is also possible to reset only a few things:

sage: a = b = c = 1
sage: reset(['a','b'])
sage: c
1
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Asked: 2013-04-28 18:09:50 -0500

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Last updated: Mar 20 '17

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