Interpolation incorrectly depends on order of data points

*To*: mathgroup at smc.vnet.net*Subject*: [mg79876] Interpolation incorrectly depends on order of data points*From*: "Andrew Moylan" <andrew.j.moylan at gmail.com>*Date*: Tue, 7 Aug 2007 01:37:35 -0400 (EDT)

The documentation of Interpolation[list] suggests that its result should be independent of the order of data points specified in list. This was the case in version 5.1 (see below). This is not the case in version 6.0.1 (Windows): Interpolation[ { {{0, 0}, 0}, {{0, 2}, 1}, {{1, 0}, 2}, {{1, 2}, 3} }, InterpolationOrder -> {1, 1} ][0, 0] returns 0, as expected, but Interpolation[ { {{1, 2}, 3}, {{0, 0}, 0}, {{0, 2}, 1}, {{1, 0}, 2} }, InterpolationOrder -> {1, 1} ][0, 0] returns 3, which is manifestly incorrect given the set of data points specified (which includes the element {{0, 0}, 0}). Here is the (correct) behaviour of version 5.1 (Linux): Interpolation[ { {0, 0, 0}, {0, 2, 1}, {1, 0, 2}, {1, 2, 3} }, InterpolationOrder -> {1, 1} ][0, 0] returns 0, as expected, and Interpolation[ { {1, 2, 3}, {0, 0, 0}, {0, 2, 1}, {1, 0, 2} }, InterpolationOrder -> {1, 1} ][0, 0] returns 0, which is also correct. Note that the format of the arguments to Interpolation was modified between versions 5 and 6. Version 6 still accepts the version 5 notation in this case. Using the version 5 notation in version 6 does not change the incorrect behaviour described above.