Issue 216 in mpmath: taylor returns wrong number of coefficients when method='quad' is used.

[mpm...@googlecode.com]

Status: New
Owner: ----

New issue 216 by warren.w...@enthought.com: taylor returns wrong number of
coefficients when method='quad' is used.
http://code.google.com/p/mpmath/issues/detail?id=216

What steps will reproduce the problem?

Here's a ipython session that demonstrates the problem:

In [1]: import mpmath as mp

In [2]: mp.mp.dps = 20

In [3]: mp.taylor(mp.sin, 0, 2)
Out[3]: [mpf('0.0'), mpf('1.0'), mpf('0.0')]

In [4]: mp.taylor(mp.sin, 0, 2, method='quad')
Out[4]: [mpf('0.0'), mpf('1.0')]

In [5]: mp.taylor(mp.sin, 0, 3)
Out[5]: [mpf('0.0'), mpf('1.0'), mpf('0.0'),
mpf('-0.16666666666666666666674')]

In [6]: mp.taylor(mp.sin, 0, 3, method='quad')
Out[6]: [mpf('0.0'), mpf('1.0'), mpf('0.0')]

In [7]: mp.__version__
Out[7]: '0.17'

What is the expected output? What do you see instead?

When the option method='quad' is used, the number of coefficients returned
by taylor is one less than it should be.

What version of the product are you using? On what operating system?

Version 0.17, Mac OSX.

[mpm...@googlecode.com]

Comment #1 on issue 216 by warren.w...@enthought.com: taylor returns wrong

number of coefficients when method='quad' is used.
http://code.google.com/p/mpmath/issues/detail?id=216

It turns out there is an off-by-one bug in diffs(). When the method is
not 'step', the 'while' statement should be 'while k < n + 1:' (rather
than 'while k < n:').

Patch attached.

Attachments:
issue216patch.diff 1.1 KB

[mpm...@googlecode.com]

Updates:
Status: Fixed

Comment #2 on issue 216 by fredrik....@gmail.com: taylor returns wrong

number of coefficients when method='quad' is used.
http://code.google.com/p/mpmath/issues/detail?id=216

Patched in r1242. Thank you very much!