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Possible bug in InverseGammaRegularized?
Posted:
Feb 26, 2013 1:09 AM


Hi, The following code gives the \delta \chi^2 for the confidence intervals as a function of the number of parameters n and desired number of sigmas m: \delta \chi^2=2 InverseGammaRegularized[n/2, 1  Erf[m/Sqrt[2]]]
The RHS can also be written as 2InverseGammaRegularized[n/2,0, Erf[m/Sqrt[2]]] (notice the 0 in the arguments)
For example, for 5 params, 1 sigma and 5 digit precision: In[1]:= n = 5; m = 1; In[2]:= N[2 InverseGammaRegularized[n/2, 1  Erf[m/Sqrt[2]]], 5] N[2 InverseGammaRegularized[n/2, 0, Erf[m/Sqrt[2]]], 5]
Out[2]= 5.8876 Out[3]= 5.8876
but when I ask for only 3 digit precision, Mathematica 9 gives the following torrent of errors in the second case:
In[4]:= N[2 InverseGammaRegularized[n/2, 1  Erf[m/Sqrt[2]]], 3] N[2 InverseGammaRegularized[n/2, 0, Erf[m/Sqrt[2]]], 3]
Out[4]= 5.8876 During evaluation of In[4]:= $RecursionLimit::reclim: Recursion depth of 1024 exceeded. >> ... (more errors) During evaluation of In[4]:= General::stop: Further output of $RecursionLimit::reclim will be suppressed during this calculation. >>
Is this a bug or am I missing something?
Cheers



