On 7/6/11 10:02 PM, robin hankin wrote:
Hi Jason
thanks for this ( I did mean 'c' not 'y'; apologies).
I didn't know about QQbar().
Why does QQbar(c) return what appears to be a numerical result, with a
question mark after it?
That is an approximation of the exact number (the question mark
signifies a small interval in which the actual number lies; see
http://www.sagemath.org/doc/reference/sage/rings/real_mpfi.html). QQbar
keeps track of the exact number, but uses interval arithmetic to take
lots of shortcuts in computations. When you ask for equality though, it
computes the result exactly.
This is similar to the Root construct in Mathematica, for example.
Thanks,
Jason
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