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Converting strings into expressions

asked 2018-02-15 13:02:49 -0600

trenzafeeds gravatar image

updated 2018-02-21 07:25:09 -0600

Hey everyone, This is probably pretty straightforward, but I couldn't find any straightforward answers with google searching. I'm looking for a function that works in the same way as python's str() and float() functions, but turns variables (especially strings) into sage's different classes of variables, like expressions. For example, if I have string variable: expression = "x1^2*x2*x3*4" and x1, x2, and x3 are already declared as variables, how can I turn that variable into a sage expression so it will work with things like the coefficient() function? Thanks!

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answered 2018-02-15 16:29:36 -0600

slelievre gravatar image

updated 2018-02-15 16:32:42 -0600

To convert a string expression to any parent X in Sage, you could do X(expression).

Thus, to convert the expression to Sage's symbolic ring, use SR(expression).

Here is how it would work with your example.

sage: x1, x2, x3 = SR.var('x1 x2 x3')
sage: expression = "x1^2*x2*x3*4" 
sage: ex = SR(expression)
sage: ex

If you prefer to work with a polynomial ring:

sage: P.<x1, x2, x3> = QQ[]
sage: f = P(expression)
sage: f
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Thank you! This worked perfect for me

trenzafeeds gravatar imagetrenzafeeds ( 2018-02-20 14:40:46 -0600 )edit

is it possible to convert a string of inequality to a sage expression?

nimaous gravatar imagenimaous ( 2018-11-02 10:19:54 -0600 )edit

@nimaous: good question. I suggest asking a new question for that.

slelievre gravatar imageslelievre ( 2018-11-02 18:55:16 -0600 )edit

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Asked: 2018-02-15 13:02:49 -0600

Seen: 188 times

Last updated: Feb 21