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MathGroup Archive 1991

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Re: Another chapter in the NeXT Tanh bug saga!

  • To: mathgroup at yoda.ncsa.uiuc.edu
  • Subject: Re: Another chapter in the NeXT Tanh bug saga!
  • From: lsf at astrosun.TN.CORNELL.EDU (Sam Finn)
  • Date: Tue, 5 Mar 91 11:11:38 EST

>Date: Mon, 4 Mar 91 13:48:41 PST
>From: jel at corp.portal.com (John Little)
>To: mathgroup at yoda.ncsa.uiuc.edu
>Subject: Re:  Another chapter in the NeXT Tanh bug saga!

>The function tanh() returns a double.  Unless you explicitly declare this
>to be the case, the result that you get will not be useful, since the compiler
>has no way of telling the type of the returned value.  Math.h says
>(among other things):
>
>extern double   tanh(/* double x */);
>
>	John
>
>
>>Well!  I've found another interesting piece of the Tanh[] puzzle!
>>
>>Stephen Wolfram made a posting implying that the Tanh bug
>>was NeXT's fault:
>>
>>> printf("%g %g\n", tanh(-1.73287), tanh(-1.73288));
>>>
>>> in a minimal C program on a NeXT under OS version 2.0 shows a
>>> discontinuity.
>>>
>>> Mathematica (apparently mistakenly) relies on built-in math functions.
>>>
>>> Stephen Wolfram <swolf at dragonfly.wri.com>
>>
>>As you will see, that word "minimal" is STRICTLY true.
>

Unless explicitly declared otherwise, constants with decimals are doubles
in c, so Wolfram's example is legitimate. (How do you declare a constant
to be a float? with a trailing f or F, as in -1.73287F)


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