Add non-offset logarithmic integral, Li

[sagetrac-myurko]

Add the logarithmic integral, Li, with integration starting at 0 rather than 2.

CC: @sagetrac-myurko @benjaminfjones

Component: calculus

Reviewer: Karl-Dieter Crisman

Issue created by migration from https://trac.sagemath.org/ticket/7357

[sagetrac-myurko]

comment:1

Attachment: li(x).patch.gz

[kcrisman]

comment:2

This is nice, but like #3401, should have some doctests indicating it works for complex input (I assume it does). The patch also depends on #3401.

[kcrisman]

comment:3

Attachment: non-offset-log-int.patch.gz

This patch adds these tests. It still depends on the (newest) patch at #3401, and in fact gets rid of one final thing which was only needed by the previous implementation of Li.

[kcrisman]

Author: Michael Yurko

[kcrisman]

Reviewer: Karl-Dieter Crisman