Thanks, I think that answered my question!
On Apr 25, 12:35 am, Robert Bradshaw <rober...@math.washington.edu>
wrote:
> On Apr 24, 2009, at 11:55 PM, Eric wrote:
>
>
>
> > Hello,
>
> > I need to be able to evaluate an expression, where the expression is
> > composed of dynamically generated variables. For example, I might have
> > a list "var_list", a list "data_list", and an expression "exprssn".
> > Here
> > 1) var_list is a list of variables, where every element in var_list
> > was created using sage.calculus.calculus.var
> > 2) data_list is a list of real numbers
> > 3) exprssn is an expression, where every variable comes from var_list
>
> > How would I evaluate exprssn when the variable var_list[i] takes the
> > value data_list[i]? If I try something like exprssn(var_list[i] =
> > data_list[i]) I get an error.
>
> > My current solution involves string generation coupled with eval
> > statements and is horribly clunky. What is the right way to do this?
>
> How about this:
>
> sage: var_list = var('x,y,z')
> sage: data_list = [2,3,5]
> sage: f = x^3 - y*z
> sage: f.subs(dict(zip(var_list, data_list)))
> -7
>
> The "zip" command takes two lists, and "zips" them together. The dict
> can take a list of 2-tuples as a constructor.
>
> sage: zip(var_list, data_list)
> [(x, 2), (y, 3), (z, 5)]
> sage: dict(zip(var_list, data_list))
> {y: 3, x: 2, z: 5}
>
> - Robert
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to sage-support@googlegroups.com
To unsubscribe from this group, send email to
sage-support-unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sage-support
URLs: http://www.sagemath.org
-~----------~----~----~----~------~----~------~--~---
