Ilya Zakharevich on Mon, 25 Sep 2000 15:36:57 -0400

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Re: power series bug

On Mon, Sep 25, 2000 at 02:18:30PM -0400, Igor Schein wrote:
> ? (acos(y)+z)^1.;
>   ***   Warning: normalizing a polynomial with 0 leading term.
>   ***   Warning: normalizing a series with 0 leading term.
>   ***   division by zero in gdiv, gdivgs or ginv
> If I pre-introduce variable z to the stack, it works fine:
> ? z^2;(acos(y)+z)^1.;
> ? 

This is easy, even I can answer it: to take a fractional power of a
series, you need to have the leading term of degree 0 - and with a
coefficient you can take a power of.  The leading
term of the second one is acos(y)*z^0 (it is a series in z), the
leading term of the first one is z*y^0 (it is a series in y).

Applying the same argument, it makes sense to take a power of acos(y),
but not of z.