Re: Bug in PadLeft/PadRight
- To: mathgroup at smc.vnet.net
- Subject: [mg109114] Re: Bug in PadLeft/PadRight
- From: "Steve Luttrell" <steve at _removemefirst_luttrell.org.uk>
- Date: Mon, 12 Apr 2010 23:04:31 -0400 (EDT)
- References: <hpkgkn$817$1@smc.vnet.net> <hputql$lhs$1@smc.vnet.net>
In the documentation for PadRight it says:
"With padding {Subscript[x, 1],Subscript[x, 2],\[Ellipsis],Subscript[x, s]}
cyclic repetitions of the Subscript[x, i] are effectively laid down and then
the list is superimposed on top of them, with the first element of the list
lying on an occurrence of Subscript[x, 1]."
That means your example PadRight[{y4, x1, x2, x3, x4}, 6, {y1, y2, y3, y4}]
works correctly.
--
Stephen Luttrell
West Malvern, UK
"David Bailey" <dave at removedbailey.co.uk> wrote in message
news:hputql$lhs$1 at smc.vnet.net...
> dh wrote:
>> Hello,
>> hope I am not fooling myself, but there seems to be a problem with
>> padding. PadLeft/PadRight seem to work as expected when used alone.
>> However if we use them sequentially there seems to be some unwanted
>> effects.
>> Consider:
>>
>> npad = 1;
>> d = d0 = {x1, x2, x3, x4};
>> d = PadLeft[d, npad + Length[d], d0]
>> d = PadRight[d, npad + Length[d], d0]
>>
>> For npad=1 padding on the right does not start with the first element of
>> d0, but with the second one.
>> For npad=2, padding starts with the third element, e.t.c.
>> If we eliminate the PadLeft, PadRight works as expected.
>> cheers, Daniel
> Well, I also get the wrong answer (using a fresh kernel) for:
>
> In[1]:= PadRight[{y4, x1, x2, x3, x4}, 6, {y1, y2, y3, y4}]
>
> Out[1]= {y4, x1, x2, x3, x4, y2}
>
> I guess you should send that to support.
>
> David Bailey
> http://www.dbaileyconsultancy.co.uk
>