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Editorial Team
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Asked: 2026-05-20T04:31:15+00:00

If you evaluate the following code twice, results will be different. Can anyone explain

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If you evaluate the following code twice, results will be different. Can anyone explain what’s going on?

findHull[points_] := Module[{},
   Needs["ComputationalGeometry`"];
   ConvexHull[points]
   ];
findHull[RandomReal[1, {10, 2}]];
Remove["Global`ConvexHull"];
findHull[RandomReal[1, {10, 2}]]
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1 Answer

  1. Editorial Team

    The problem is that even though the module is not evaluated untill you call findHull, the symbols are resolved when you define findHull (i.e.: The new downvalue for findHull is stored in terms of symbols, not text).
    This means that during the first round, ConvexHull resolves to Global`ConvexHull because the Needs is not evaluated.
    During the second round, ComputationalGeometry is on $ContextPath and so ConvexHull resolves as you intended.

    If you really cannot bear to load ComputationalGeometry beforehand, just refer to ConvexHull by its full name: ComputationalGeometry`ConvexHull. See also this related answer.

    HTH

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