BUG: Intersect[] can't use a variable as intersection index for 3D intersections

Rulatir shared this question 3 years ago

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In both Geogebra 5 and 6 the Intersect command refuses to store an expression defining the intersection index when the intersection involves 3D surfaces (at least hyperbolic paraboloids, possibly all quadrics). Whatever expression I put there, it gets immediately evaluated to a number, and that number is stored in the definition.

This is inconsistent with the behavior for 2D intersections.

The way it hurts me is by preventing me from creating a tool that would accept intersection index as a parameter. Not being a Geogebra Merlin who can write tools in code, I must first create an example output object, and then use it to create the tool. However the intersection index argument gets hard-bound, and I have no way to specify it as an input when I create the tool; the variable where I put the intersection index is not offered as a possible input object, because the output object doesn't actually depend on it, having hard-bound its value at the time of definition.

Repro: https://www.geogebra.org/m/cyqyfrym

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Comments (5)

ccambre ● 3 years ago

I can't run 100m in less than 10". This is not a bug. And indeed Intersect can't handle with all possible types of objects either

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Rulatir ● 3 years ago

This is not a case of running 100m in less than 10s. This has nothing to do whatsoever with computational difficulty. The expression for the intersection index only has to be evaluated once before the output of the tool can be computed. There is no difference in computational effort between evaluating that expression at definition time and evaluating it at the time the object itself is evaluated. Doing so in some contexts but not doing so in other very similar contexts is just pure inconsistency without any rationale or justification whatsoever.

When "intersect can't handle with all possible types of objects", it refuses to accept the definition and shows a dialog that lists allowed combination of types. If using a dynamic expression for intersection index is not supported when working with 3D objects, it should likewise show that same dialog and refuse to accept the definition.

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