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what's wrong with these expressions?

  • To: mathgroup at
  • Subject: [mg104606] what's wrong with these expressions?
  • From: dushan <dushanm at>
  • Date: Wed, 4 Nov 2009 01:41:31 -0500 (EST)

I defined two 3-D vector functions,
    {Subscript[n,p][z_], Subscript[n,m][z_]} := {{p1[z],p2[z],p3[z]},
where p? and m? are simple functions of z.  When displayed they appear
as expected.  But when I tried to define the dyadics
    {Subscript[nn,p][z_], Subscript[nn,m][z_]} :=
                     {Outer[Times, Subscript[n,p][z], Subscript[n,p]
                      Outer[Times, Subscript[n,m][z], Subscript[n,m]
I got the error message that the expression 'is incomplete, more input
is needed'.

When I separate this into two independent commands, as
    Subscript[nn,p][z_] := Outer[Times, Subscript[n,p][z],
    Subscript[nn,m][z_] := Outer[Times, Subscript[n,m][z],
no error is generated.  Probably irrelevant, but I noticed that in
both cases the outer brackets of the 'm' definition were slightly
smaller than those of the 'p' definition.

To check the result I asked to display the inner product
and got the error message 'Recursion depth 256 exceeded'.

In fact, when, to reassure myself, I tried again to display Subscript
[n,p][z], I got the same error message.  So I went back over the
definitions, and this time
produced the expected answer.

What could possibly be changing that sometimes, but not always,
produces the error messages in these two cases?  I'm at a loss to know
what to watch out for.

- Dushan

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