Integrating a simple interpolated function as follows generates invalid comparison errors.
In[545]:= f= Interpolation[{{0., 0.}, {1., 1.}}, InterpolationOrder -> 1];
NIntegrate[f[0.5 + 0.5 x^2], {x, 0.0, 1.0}]
During evaluation of In[545]:= Less::nord: Invalid comparison with 0. -1. I attempted. >>
During evaluation of In[545]:= Less::nord: Invalid comparison with 0. -1. I attempted. >>
During evaluation of In[545]:= Less::nord: Invalid comparison with 0. -1. I attempted. >>
During evaluation of In[545]:= General::stop: Further output of Less::nord will be suppressed during this calculation. >>
Out[546]= 0.666667
It seems that Mathematica tries to find a root of the argument in the function. Why? And how can it be prevented?
Method -> "AdaptiveQuasiMonteCarlo"to rid yourself of warnings. – ciao Mar 17 '14 at 07:39