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derivatives of indexed variables

• To: mathgroup at smc.vnet.net
• Subject: [mg2626] derivatives of indexed variables
• From: george at mech.seas.upenn.edu ( George Jefferson )
• Date: Sun, 3 Dec 1995 02:51:57 -0500

What am I missing?

total derivative of unspecified y:

In[1]:= Dt[y,x]

Out[1]= Dt[y, x]

But if we take the derivaitve of an undefined indexed variable
it is assumed to be a constant..

In[2]:= Dt[a[1],x]

Out[2]= 0

note however that the indexed symbol could easily represent a non-constant.

In[3]:= a[1]=y; Dt[a[1],x]

Out[3]= Dt[y, x]


clearly the trouble is that there is no distinction between an indexed
symbol and a function evaluated at a fixed point..
Is there a workaround?