cygwin: robert miller's 2-descent is completely broken on cygwin

[williamstein]

sage -t  "devel/sage/sage/schemes/elliptic_curves/descent_two_isogeny.pyx"
**********************************************************************
File "/home/wstein/sage-4.4.3/devel/sage/sage/schemes/elliptic_curves/descent_two_isogeny.pyx", line 1093:
    sage: log(n1,2) + log(n1_prime,2) - 2 # the rank
Expected:
    1
Got:
    0
**********************************************************************
File "/home/wstein/sage-4.4.3/devel/sage/sage/schemes/elliptic_curves/descent_two_isogeny.pyx", line 1098:
    sage: log(n1,2) + log(n1_prime,2) - 2 # the rank
Expected:
    2
Got:
    0
**********************************************************************
File "/home/wstein/sage-4.4.3/devel/sage/sage/schemes/elliptic_curves/descent_two_isogeny.pyx", line 1102:
    sage: log(n1,2) + log(n1_prime,2) - 2 # the rank
Expected:
    3
Got:
    2*log(3)/log(2) - 2
**********************************************************************
File "/home/wstein/sage-4.4.3/devel/sage/sage/schemes/elliptic_curves/descent_two_isogeny.pyx", line 1195:
    sage: log(n1,2) + log(n1_prime,2) - 2 # the rank
Expected:
    1
Got:
    0
**********************************************************************
File "/home/wstein/sage-4.4.3/devel/sage/sage/schemes/elliptic_curves/descent_two_isogeny.pyx", line 1198:
    sage: log(n1,2) + log(n1_prime,2) - 2 # the rank
Expected:
    2
Got:
    0
**********************************************************************
File "/home/wstein/sage-4.4.3/devel/sage/sage/schemes/elliptic_curves/descent_two_isogeny.pyx", line 1201:
    sage: log(n1,2) + log(n1_prime,2) - 2 # the rank
Expected:
    3
Got:
    log(3)/log(2) - 1
**********************************************************************
2 items had failures:
   3 of  30 in __main__.example_18
   3 of  11 in __main__.example_19
***Test Failed*** 6 failures.
For whitespace errors, see the file /home/wstein/.sage//tmp/.doctest_descent_two_isogeny.py
 [29.1 s]

CC: @jpflori @dimpase @kcrisman

Component: porting: Cygwin

Reviewer: Karl-Dieter Crisman

Issue created by migration from https://trac.sagemath.org/ticket/9174

[kcrisman]

comment:1

This file passed doctests in a build of mine on XP.

[kcrisman]

Reviewer: Karl-Dieter Crisman

[kcrisman]

comment:2

And checking by hand works.

Since this was undoubtedly an XP machine on which the original failure was reported, I will move this to sage-invalid.

[kcrisman]

comment:4

But doing anything other than the first one by hand doesn't work. In fact, nasty things happen.

[kcrisman]

comment:5

I attempted this, but got forking errors; that doesn't mean it doesn't actually work. JP, want to give it a whirl?

[jpflori]

comment:6

And the test passes for me (64bits W7 + 5.6.rc0).

[kcrisman]

comment:7

And the test passes for me (64bits W7 + 5.6.rc0).

Don't forget to try these by hand as well. In the past I've had failures only in the terminal.