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Numerical approximation for expression coefficients

asked 2011-04-28 00:38:22 -0500

Grover gravatar image

updated 2011-04-28 12:04:17 -0500

Kelvin Li gravatar image

I currently have an equation that looks like

x = 4/5(4y - 3)*z - 1/3

How can I get Sage to convert the coefficients to numerical approximations? I want to end up with something like

x = 0.8(4y - 3)*z - 0.333333333

I tried x.n(), but that only gives a "cannot evaluate symbolic expression numerically" error. Also x*1.0 doesn't do anything.

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Since 1.2*x does what you want (well, except being multiplied by 1.2!), but not 1.0*x, I wonder if there is a bug here. See for a post about this on sage-devel.

kcrisman gravatar imagekcrisman ( 2011-04-28 03:13:05 -0500 )edit

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answered 2011-04-28 08:10:54 -0500

Kelvin Li gravatar image

If $x$ is to be treated as a polynomial, then the following might suit your needs:

sage: var('y z')
(y, z)
sage: x = 4/5*(4*y - 3)*z - 1/3
sage: x.polynomial(RR)
3.20000000000000*y*z - 2.40000000000000*z - 0.333333333333333


sage: RR?

for more information about RR

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Asked: 2011-04-28 00:38:22 -0500

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Last updated: Apr 28 '11