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Re: Re: Differentiation problem/bug?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg69863] Re: [mg69783] Re: Differentiation problem/bug?
*From*: Paul Abbott <paul at physics.uwa.edu.au>
*Date*: Tue, 26 Sep 2006 00:59:22 -0400 (EDT)
*References*: <eevrea$gfd$1@smc.vnet.net> <200609230844.EAA22439@smc.vnet.net> <1159172183.1427.12.camel@acus.itpa.lt>
On 25/9/06, Arturas Acus wrote:
> > I never use NonConstants. Also, it is a good idea to avoid using
>> variables involving capital letters. For calculations where there is
>> implicit dependence with respect to a variable I use Dt instead.
>>
>> inp = 1/4 + 3/8/E^(2 I f) + (3/8) E^(2 I f) - (1/4) E^(-2 I f - I t) +
>> (1/4) E^(2 I f - I t) - (1/4) E^(I t - 2 I f) + (1/4) E^(2 I f + I t) +
>> (1/16) E^(-2 I f - 2 I t) + (1/16) E^(2 I f - 2 I t) +
>> (1/16) E^(2 I t - 2 I f) + (1/16) E^(2 I f + 2 I t) -
>> 1/8/E^(2 I t) - (1/8) E^(2 I t)
>>
>> Dt[t, r] ^= 0;
>>
>> Dt[inp, r] // FullSimplify
>>
> > Cheers,
> > Paul
>
>Could Your share any thoughts why this way is more preferable.
Because it is simple, reliable, and direct.
>For example, using Dt I should explicitly write down rules not only for
>independent variables, but for model parameters also. Thus model
>variables and parameters mixes up, which for my opinion doesn't look
>nice from the point of view of logical consistence.
No. Use
SetAttributes[{a, b, c, ...}, Constant]
for (constant) model parameters.
So, for example, for model parameters a and b,
SetAttributes[{a, b}, Constant]
and for independent variables x and y,
Dt[y, x] ^= 0; Dt[x, y] ^= 0
then compute
Dt[a x + b y, x]
Cheers,
Paul
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