Hi William

On Wed, Sep 02, 2009 at 11:18:40PM -0700, William Stein wrote:
>    If you take any integer (or rational) alpha such that alpha is not a
>    perfect square, and try to compute sqrt(alpha), Sage promotes alpha to the
>    symbolic ring (SR) and takes the square root there.  Thus the first is
>    correct, since sqrt(-1) is not in ZZ, so the square root is instead taken
>    in the symbolic ring, which yields I. 

OK

>    In the second case, the expression z=1.+sqrt(-1.) is in the complex real
>    field with 53 bits precision.  The *base ring* of that field is the real
>    field with 53 bits precision.  Maybe you were instead thinking about the
>    parent of z?

Thanks

sage: z=1.+sqrt(-1); print z; z.parent()
1.00000000000000 + 1.00000000000000*I
Symbolic Ring
sage: z=1.+sqrt(-1.); print z; z.parent()
1.00000000000000 + 1.00000000000000*I
Complex Field with 53 bits of precision
sage: 

regards,
Jan
-- 
   .~. 
   /V\     Jan Groenewald
  /( )\    www.aims.ac.za
  ^^-^^ 

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