Re: Curious behavior of Taylor series

On 21 Aug 2006 21:21:36 +0200, Martin Rubey <[email protected]> wrote:
> "Igor Khavkine" <[email protected]> writes:
>
> > I've filed a bug report (#312) and I have a tentative fix for it. But I'm
> > having trouble testing it. I've copied the culprit file algebra/sttaylor.spad
> > into my current working dir and modified it.  Issuing the command )compile
> > sttaylor compiled the file. However, the old definition of sqrt is still
> > being invoked. How do I force the code from sttaylor.spad in my working
> > directory to take priority?
>
> That's very strange, usually, after compilation, the new definition replaces
> the old. You can also say

You're right, that's what was happening. But my initial modification
was in the wrong place, so it wasn't being triggered. But I've found
the right place for it and it seems to work.

> I suspect you modified powern?
>
> Maybe you could send me the modification, then I can look at it.

I'm attaching the patch. It's very small. The original author simply
forgot to prepend the leading zeros before returning the power series.

> BTW: Thanks a lot for looking at this!

No problem.

Igor

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diff -ur axiom-20050901/src/algebra/sttaylor.spad.pamphlet axiom-20050901.new/src/algebra/sttaylor.spad.pamphlet
--- axiom-20050901/src/algebra/sttaylor.spad.pamphlet	2005-01-30 07:03:10.000000000 -0500
+++ axiom-20050901.new/src/algebra/sttaylor.spad.pamphlet	2006-08-21 15:49:25.000000000 -0400
@@ -448,6 +448,9 @@
 
           RATPOWERS => co**rn * YS(powerrn(rn,(invCo :: A) * x,#1))
           error "** rational power of coefficient undefined"
+        zeropref : ST A := new(ord::I::NNI,0::A)$LA :: ST A
+        concat(zeropref, power)
+
 
     if A has Field then
       mapdiv(x,y) == delay