Re: Strange bug
- To: mathgroup at smc.vnet.net
- Subject: [mg53288] Re: Strange bug
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Tue, 4 Jan 2005 03:13:49 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
On 1/3/05 at 4:29 AM, stevebg at adelphia.net (Steve Gray) wrote:
>I have procedural function "ordermat." It works ok if the
>next-to-last (useless) line is there but if I remove that one line,
>I get error messages due to the last line, at execution time:
>Set::write: Tag Times in Null\{0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
>\[LeftSkeleton]1\ \[RightSkeleton]} is Protected.
>("intersect" returns a small integer and computes "tafr.")
>I've seen bugs like this before. I'm using 5.0.1.0 with Windows.
>Any clues? Thanks in advance.
>ordermat[gon_] := Module[{row, rx, cx},
> gonl = Length[gon];
> matx = Table[0, {i, 1, gonl}, {j, 1, gonl}];
> gona = Join[gon, gon];
> For [ rx = 1, rx <= gonl, rx++,
> row = Table[0, {2*gonl}];
> row[[rx]] = 1;
> row[[rx + 1]] = 2;
> ab = gona[[rx]];
> ae = gona[[rx + 1]];
> For [ cx = 1, cx <= gonl - 3, cx++,
> bb = gona[[cx + rx + 1]];
> be = gona[[cx + rx + 2]];
> int = intersect[ab, ae, bb, be];
> If [ int == 3, row[[cx + rx + 1]] = tafr + 1];
> ]
> rx; (* Error unless some expression is here.?? *)
> matx[[rx]] = Table[Max[row[[i]], row[[i + gonl]]], {i, gonl}];
> ]
> ]
As near as I can tell, this code simply creates a square matrix whose first row is {1,2,0,0...} and every subsequent row is rotated one position right. If so, the following code does the same thing much more efficiently
ordermat[n_]:=
Module[{row = PadRight[{1, 2}, n]},
Join[{row}, RotateRight[row, #1]&/@Range[n-1]]]
and
matx = ordermat[Length@gon]
produces the same result as your code.
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