# Ticket #12815: 12815_tolerance_doc.patch

File 12815_tolerance_doc.patch, 2.4 KB (added by jdemeyer, 7 years ago)
• ## doc/en/developer/conventions.rst

# HG changeset patch
# User Jeroen Demeyer <jdemeyer@cage.ugent.be>
# Date 1357636755 -3600
# Node ID 0d68a886ccf3a651fd5bfd92f11c55a59bed3d75
# Parent  7b89b8deffb55ebc7951552bbbf3d2009b8e97ec
Fix documentation for "tolerance" doctests

diff --git a/doc/en/developer/conventions.rst b/doc/en/developer/conventions.rst
 a 0.0 The 8-th cyclotomic field is generated by the complex number e^\frac{i\pi}{4}.  Here we compute a numerical approximation. The value provided in the source of the doctest (0.707106781186548 + 0.707106781186547*I), and the value computed by the tested instance of Sage (N(zeta8)) are subtracted from each other and fed into the abs() function for comparison to the tolerance.  So the only prerequisite for using this feature is that the abs() function may be applied. Of course, for a relative tolerance, division must also be possible. :: e^\frac{i\pi}{4}.  Here we compute a numerical approximation:: sage: K. = CyclotomicField(8) sage: N(zeta8)                             # absolute tolerance 1e-15 0.707106781186548 + 0.707106781186547*I sage: N(zeta8)                             # absolute tolerance 1e-10 0.7071067812 + 0.7071067812*I A relative tolerance on a root of a polynomial.  Notice that the root should normally print as 1e+16, or something similar. However, the tolerance testing causes the doctest framework to use the output in a *computation*, so any valid text representation of the predicted value may be used. **This is actually broken**, see :trac:12815. :: The "tolerance" feature checks for floating-point literals, which may occur anywhere in the doctest output, for example as polynomial coefficients:: sage: y = polygen(RDF, 'y') sage: p = (y - 10^16) * (y - 10^-13) * (y - 2) sage: p.roots(multiplicities=False)[2]     # relative tol 1e-10 1e16 sage: p = (y - 10^10) * (y - 1); p y^2 - 10000000001.0*y + 10000000000.0 sage: p                           # rel tol 1e-9 y^2 - 1e10*y + 1e10 -  If a line contains todo: not implemented, it is never tested. It is good to include lines like this to make clear what we