       Re: Error in FullSimplify

• To: mathgroup at smc.vnet.net
• Subject: [mg122942] Re: Error in FullSimplify
• From: "Dr. Wolfgang Hintze" <weh at snafu.de>
• Date: Thu, 17 Nov 2011 07:02:25 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <ja2psp\$ma5\$1@smc.vnet.net>

```This can indeed be easily explained. You didn't take apropriate care of
operator priorities.
In your case the last FullSimplify acts on 4. which is most probably
Hence either put brackets around the whole expression or use the
function form FullSimplify[]

In:=
FullSimplify[-E^((a + b*I)*x) + E^((a - b*I)*x) +
E^((-a + b*I)*x) - E^((-a - b*I)*x) /. a -> 3 /.
b -> 4]
Out=
-4*I*Sin[4*x]*Sinh[3*x]

In:=
FullSimplify[-E^((a + b*I)*x) + E^((a - b*I)*x) +
E^((-a + b*I)*x) - E^((-a - b*I)*x) /. a -> 3. /.
b -> 4.]
Out=
-4*I*Sin[4.*x]*Sinh[3.*x]

Hence it was not an error in FullSimplify but an error in the usage of
it.

Best regards,
Wolfgang

"Philipp Weißgraeber" <=?ISO-8859-15?Q?Philipp_Wei=DFgraeber?=> schrieb
im Newsbeitrag news:ja2psp\$ma5\$1 at smc.vnet.net...
> Hello
>
> I have experienced some strange error in the FullSimplify-function in
> Mathematica 7.
>
> Input:
> (-E^((a+b I)x)+E^((a-b I)x)+E^((-a+b I)x)-E^((-a-b I)x))/.a->3 /.b->4
> //
> FullSimplify
> (-E^((a+b I)x)+E^((a-b I)x)+E^((-a+b I)x)-E^((-a-b I)x))/.a->3.
> /.b->4.
> // FullSimplify
>
> Output:
> -4 I Sin[4 x] Sinh[3 x]
> -2 I Sin[4. x] Sinh[3. x]
>
> And the later result is wrong.
>
> What happens here, how can this be explained?
>
> CU
>
> Philipp
>

```

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