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

**References**:**Re: Differentiation problem/bug?***From:*Paul Abbott <paul@physics.uwa.edu.au>