4
$\begingroup$

Bug introduced in 9.0 or earlier and fixed in 11.1.0


This works fine:

Derivative[0, 1, 0, 0][Hypergeometric2F1][1, 0, 2,  I/10^15 + 447.57809534442]

and gives -5.08798 + 3.13457 I within tiny milliseconds as expected. However, with this input

Derivative[0, 1, 0, 0][Hypergeometric2F1][1, 0, 2,  I/10^15 + 447.578095344423]

Mathematica hangs for several minutes, so I have no enough patience to wait for the answer. What is the reason and how I can overcome this behaviour?

I use Mathematica 10.2.0 for Mac OS X x86 (64-bit) (July 7, 2015). Just checked this example with Mathematica 8 on Linux and all works fine, so this issue is version/OS specific.

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6
  • 3
    $\begingroup$ The problem is present also on 11.0. $\endgroup$
    – kirma
    Aug 19, 2016 at 16:35
  • 3
    $\begingroup$ Yes, the problem is present on 11.0.0 under Windows $\endgroup$
    – user58955
    Aug 19, 2016 at 16:36
  • 1
    $\begingroup$ And I just checked that the problem is present in Wolfram Cloud $\endgroup$ Aug 19, 2016 at 16:36
  • $\begingroup$ It works in 5.2, tho. $\endgroup$ Aug 19, 2016 at 17:30
  • 1
    $\begingroup$ I'm a bit surprised it doesn't take the derivative symbolically first. Derivative[0, 1, 0, 0][Hypergeometric2F1][1, 0, 2, x] is equal to 1 - Log[1 - x] + Log[1 - x]/x. $\endgroup$
    – QuantumDot
    Aug 22, 2016 at 19:44

1 Answer 1

1
$\begingroup$
$Version

(*  "11.0.0 for Mac OS X x86 (64-bit) (July 28, 2016)"  *)

Derivative[0, 1, 0, 0][Hypergeometric2F1][1, 0, 2, 
  I/10^15 + 447.57809534442] // AbsoluteTiming

(*  {0.065291, -5.08798 + 3.13457 I}  *)

For the second case, use arbitrary-precision rather than machine precision

Derivative[0, 1, 0, 0][Hypergeometric2F1][1, 0, 2, 
  I/10^15 + 447.578095344423`15] // AbsoluteTiming

(*  {0.048323, -5.0879817774139 + 3.1345735597461 I}  *)
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2
  • $\begingroup$ But how I can setup Mathematica to use arbitrary-precision rather than machine precision automatically? I can't just insert "`15" manually to each number that appears in my program and external libraries that I use. $\endgroup$ Aug 19, 2016 at 18:09
  • $\begingroup$ @StanislavPoslavsky As a fix, it should be enough to do the conversion before calling this function. Computing x * 1`15 should do it. I don't know how to convert back to machine-precision though. $\endgroup$
    – masterxilo
    Aug 22, 2016 at 18:30

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