Interpolation does not quite interpolate

*To*: mathgroup at smc.vnet.net*Subject*: [mg81822] Interpolation does not quite interpolate*From*: Neil Stewart <neil.stewart at warwick.ac.uk>*Date*: Thu, 4 Oct 2007 04:24:43 -0400 (EDT)*Reply-to*: Neil Stewart <neil.stewart at warwick.ac.uk>

I'm having trouble with Interpolation[]. With InterpolationOrder->0, Interpolation[] returns a function that fails to "agree with data at every point" as promised in the manual. When InterpolationOrder->1 or higher, the problem disappears. Here is an example. Notice that although the point {1,1} is specified f[1] = 2. In[1]:= f = Interpolation[{{1, 1}, {2, 2}, {3, 3}}, InterpolationOrder -> 0] Out[1]= InterpolatingFunction[{{1, 3}}, <>] In[2]:= f[1] Out[2]= 2 (* f[1] should be 1 *) In[3]:= f[2] Out[3]= 2 In[4]:= f[3] Out[4]= 3 In[5]:= g = Interpolation[{{1, 1}, {2, 2}, {3, 3}}, InterpolationOrder -> 1] Out[5]= InterpolatingFunction[{{1, 3}}, <>] In[6]:= g[1] Out[6]= 1 (* f[1] is 1 now *) In[7]:= g[2] Out[7]= 2 In[8]:= g[3] Out[8]= 3 Is this a bug? Can anyone help? Thanks, Neil