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numeric approximation??

asked 2011-09-26 14:53:39 -0600

nalaurethsulfate gravatar image

updated 2011-09-26 15:02:49 -0600

So I have an equation that solved (symbolically) looks something like this:

r == 1/488486532917088881338043645348028612608*sqrt(1271541785242875384103984923680382406444427305742938801212457) - 80406364132947/169706962694363951398912

and when I do anything to evaluate this numerically I get a TypeError? Right now I am copying and pasting this output into wolfram alpha, but really there has to be a better way?

Furthermore if I try to evaluate the equation with find_root(...) I get this error:

File "expression.pyx", line 984, in sage.symbolic.expression.Expression.__float__ (sage/symbolic/expression.cpp:5596) TypeError: unable to simplify to float approximation

?!

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Can you post the code that produces the solution r?

benjaminfjones gravatar imagebenjaminfjones ( 2011-09-26 16:11:05 -0600 )edit

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answered 2011-09-26 16:47:30 -0600

DSM gravatar image

My guess is that you're trying to call .n() or float not on the number but on the _equation_. For example:

sage: ans = solve((x-11/sqrt(13))**2,x)
sage: ans
[x == 11/13*sqrt(13)]
sage: ans[0]
x == 11/13*sqrt(13)
sage: ans[0].n()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
[...]
/Applications/sage/local/lib/python2.6/site-packages/sage/symbolic/expression.so in sage.symbolic.expression.Expression._numerical_approx (sage/symbolic/expression.cpp:17880)()
TypeError: cannot evaluate symbolic expression numerically

You really want to get at the expression on the right:

sage: ans[0].rhs().n()
3.05085107923876

or maybe

sage: ans = solve((x-11/sqrt(13))**2,x,solution_dict=True)
sage: ans[0]
{x: 11/13*sqrt(13)}
sage: ans[0][x]
11/13*sqrt(13)
sage: ans[0][x].n()
3.05085107923876
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Wow thanks. Worked like a charm. I was thinking that may be my problem, but didn't know how to access that. Thanks again.

nalaurethsulfate gravatar imagenalaurethsulfate ( 2011-09-26 19:21:03 -0600 )edit

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Asked: 2011-09-26 14:53:39 -0600

Seen: 3,191 times

Last updated: Sep 26 '11