[sage-support] Re: expression evaluation with dynamically generated variables
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
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[sage-support] Re: expression evaluation with dynamically generated variables
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
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