Charles
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 Dec4 comment Inverse of LogIntegral Works great, thanks! I tweaked the WorkingPrecision and PrecisionGoal upward and all was good. Dec4 accepted Inverse of LogIntegral Dec4 comment Inverse of LogIntegral @DanielLichtblau: Thanks. (Maybe that should be an answer.) Mathematica is still giving me answers I don't believe (say, integrating up to 10^200 giving an answer of 2*10^7 instead of < 0.1) but at this point it seems hopeless. At least it works for small numbers. Dec4 comment Inverse of LogIntegral (The true answer should be about 0.01125, or 19 orders of magnitude smaller.) Dec4 comment Inverse of LogIntegral @DanielLichtblau: That's not a sensible answer, though. The li^{-1}(x) > x (in fact ~ x log x), so the integral should be less than the integral of 1/x over the same region, which is about 4.6. Dec4 comment Inverse of LogIntegral @Artes: With an NIntegrate::inumr error. I've edited in code. Dec4 revised Inverse of LogIntegral expand, as requested Dec4 asked Inverse of LogIntegral Aug5 comment Use of Strassen's algorithm @TysonWilliams: BLAS does use Strassen in DGEMMS*. But Daniel's description of why to avoid that algorithm for floating-point calculations is apt. Jul2 awarded Curious May28 awarded Nice Question May22 comment How do I get Mathematica to return a function call unevaluated? Hah! So at least I wasn't too far off the mark, just careless. Thanks for pointing this out! May22 awarded Yearling May22 comment How do I get Mathematica to return a function call unevaluated? @gpap: What do you get for AlgebraicQ /@ {7, Pi, Pi + E, I}? May22 comment How do I get Mathematica to return a function call unevaluated? @gpap: I can't imagine how, honestly. I mean, clearly that should work if I gave it a non-Real, but for a Real it should return Element[x, Algebraics] because that's what you're telling it to return. Very strange, I'd be interested to learn more about this case. May22 revised How do I get Mathematica to return a function call unevaluated? final answer May22 revised How do I get Mathematica to return a function call unevaluated? flesh out May22 accepted How do I get Mathematica to return a function call unevaluated? May22 comment How do I get Mathematica to return a function call unevaluated? @m_goldberg: The built-in AlgebraicIntegerQ has precisely the same behavior I'm describing. (How could a function possibly guarantee to return True or False when the answer is not even known to mathematicians?) May22 revised How do I get Mathematica to return a function call unevaluated? add image