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Strange bug

• To: mathgroup at smc.vnet.net
• Subject: [mg53255] Strange bug
• From: Steve Gray <stevebg at adelphia.net>
• Date: Mon, 3 Jan 2005 04:29:31 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

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.

Steve Gray



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}];
           ]
    ] 

• Follow-Ups:
  • Re: Strange bug
    • From: DrBob <drbob@bigfoot.com>