## reduce-algebra-developers — Discussion of development, administration and support for Reduce

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 Re: [Reduce-algebra-developers] Commutation between sum and df. From: abpetrov - 2013-09-10 17:58:11 ```Of course, you are right. Thank you. 09.09.2013 19:48, Rainer Schöpf пишет: > On Sat, 7 Sep 2013 at 20:58 -0000, abpetrov wrote: > > > Hi, > > I tried to define an commutation rule for operation sum and operator df. > > It looks quite simple, but don't works. > > Why this rule don't work. > > Program with that rule is below, it looks simple, so without comments. > > > > > > off lower\$ > > > > operator H,k,x; > > H := sum( (1/2)*k(i)*x(i)**2, i, -infinity,infinity); > > r1 := {df(sum( ~~f, ~~i, ~~i1,~~i2),~~x(~~i)) => sum( df(f, x(i)) , i, > > i1,i2)}; > > (df(H,x(i)) where r1); > > I've just corrected the handling of the sum operator and committed. > > Besides, your rule doesn't make sense, it should be > > r1 := {df(sum(~f,~i,~i1,~i2),~x) => sum(df(f,x),i,i1,i2)}; > > Rainer > ```

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