Endless symbolic computation

[sagetrac-ipasquinelli]

I tried calculating

a=e^(I*pi/4)+1
b=1-e^(I*pi/4)
a*b

and both expressions a*b and a/b don't stop computing.

I tried both on sage-8.1 for Windows and on sage-8.2.beta6 on Ubuntu (native Ubuntu desktop on Windows10).

Depends on #24838

CC: @rwst @videlec

Component: symbolics

Keywords: days93, days94

Author: Irene Pasquinelli

Branch/Commit: 4d0c51e

Reviewer: Ralf Stephan, Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/24883

[videlec]

comment:1

Could you add your architecture/sage version in the ticket description? I can confirm the behavior on archlinux with compiled sage-8.2.beta6.

[videlec]

comment:2

Alternative computation that terminates:

UCF = UniversalCyclotomicField()
a = UCF.zeta(8) + 1
b = 1 - UCF.zeta(8)
a * b

[sagetrac-ipasquinelli]

Description changed:

--- 
+++ 
@@ -9,3 +9,5 @@
 ```
 
 and both expressions a*b and a/b don't stop computing. 
+
+I tried both on sage-8.1 for Windows and on sage-8.2.beta6 on Ubuntu (native Ubuntu desktop on Windows10).

[sagetrac-sdrewitz]

comment:4

I can confirm it on archlinux with compiled sage-8.2.beta6, sage-8.2.beta5 and sage-8.1.
However, with the sagemath 8.1-11 from the archlinux community repository it does work.

sage: a = 1 + e^(I*pi/4)
sage: b = 1 - e^(I*pi/4)
sage: a*b
1/4*((I + 1)*sqrt(2) - 2)*(-(I + 1)*sqrt(2) - 2)
sage: a/b
-1/2*(-(I + 1)*sqrt(2) - 2)/(-(1/2*I + 1/2)*sqrt(2) + 1)

[rwst]

comment:5

Confirmed in beta6. The loop is in Pynac. Thanks for the report.

[rwst]

comment:6

Actually there were changes in pynac-0.7.17 that appear to have fixed it. With #24838:

sage:  sage: a = 1 + e^(I*pi/4)
....:  sage: b = 1 - e^(I*pi/4)
....:  sage: a*b
....: 
1/4*((I + 1)*sqrt(2) - 2)*(-(I + 1)*sqrt(2) - 2)

We might doctest this in this ticket, though.

[videlec]

comment:7

Replying to @rwst:

Actually there were changes in pynac-0.7.17 that appear to have fixed it. With #24838:

Cool

We might doctest this in this ticket, though.

+1

[videlec]

Author: Irene Pasquinelli

[videlec]

comment:8

Ralf, Irene is working on this ticket (she is learning how to develop). We will have a branch in a minute. Thanks for pointing #24838.

[sagetrac-ipasquinelli]

Branch: u/ipasquinelli/24883

[sagetrac-ipasquinelli]

New commits:

e470685	version / chkum / rm patch
d3511ce	24838: doctest fixes
efe5f14	24883: adding doctest for symbolic