Possible Mathematica 4.0 bug

• To: mathgroup at smc.vnet.net
• Subject: [mg30786] Possible Mathematica 4.0 bug
• From: Christian Mikkelsen <chr_mikkelsen at yahoo.com>
• Date: Wed, 19 Sep 2001 00:16:25 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```The following problem cost most of a mornings work and
I ended up attributing it to a bug but before I send
it off to Wolfram Research I'd like some comments.

I have a polynomial defined as

H[z_]= (1/z^6)
((0.17897972007618376+0.1832666067995157
I)((0.07806788263644916+0.9898486037537829 I)+I
z)((-1.0304811754750547-1.1012670896195078
I)+z)((-0.4716966687204682-0.6843778680006037
I)+z)((-0.4537703518350889+0.7354674436955
I)+z)((-0.32047121654063226+0.18872779388498095
I)+z)((0.7411819790476893+0.15538114678579676 I)+z));

with some auxiliary definitions

f[w_] = Arg[H[Exp[I w]]];
fmm[w_] = (f[w+h]-2f[w]+f[w-h])/h^2 /.h->10^(-6) //
Simplify;
d = 1 10^8;

The following results in an erroneous(?)
simplification

disp[l_]=fmm[d/l] //Simplify

but defining d = 1.0 10^8 gives the correct(?) result.
A different result at any rate. Ok, so in principle I
have a workaround but I would be happy to know if the
issue also exists in version 4.1. I don't currently

Finally, it is of course possible that I have missed
something so I would be most happy to get feedback on
that as well.

Cheers,

Christian Mikkelsen

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```

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