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Getting the Derivative of an HoldForm Expression
Hi, am currently fiddling with some equations. To make it more easy I want to introduce subexpressions which should not be evaluated. For this purpose I found HoldForm. But this creates some weird results when I want to get the derivative of such a term. But let's have a look at an example: In1:=T=HoldForm[2*a[t]] Out1=2 a[t] In2:= a[t]=b[t]+c[t] Out2=b[t]+c[t] In3:=T Out3=2 a[t] <-- this is what I need HoldForm for, as I do not want 2(b[t]+c[t]) as result In4:=D[T,t] Out4=2 a'[t] HoldForm'[2(b[t]+c[t])] I would expect 2 a'[t] as result so the term HoldForm'[...] seems to be a bit weird to me. Can anyone explain to me how I can avoid this term? Thanks in advance.