       Re: Variables in Iterator limits?

• To: mathgroup at smc.vnet.net
• Subject: [mg109645] Re: Variables in Iterator limits?
• From: AES <siegman at stanford.edu>
• Date: Mon, 10 May 2010 06:37:39 -0400 (EDT)
• Organization: Stanford University
• References: <hs67fk\$2rh\$1@smc.vnet.net>

```To make this query a bit more generic, suppose you're typing in at the
beginning of a notebook a series of expressions that you're going to use
later on

expr1  :=  . . .
expr2  :=  . . .
expr3  :=  . . .
. . .

where each of these expressions contains some subset of a fairly lengthy
set of global variables a, b, c, . . . to which no values have yet been
assigned.

Suppose further that as you're typing in these expressions, you may to
test whether one or another of them (let's say expr2) works properly,
without having any persistent side effects on that expression, or any of
the previous or subsequent expression definitions, or any of the global
variables, after the test is carried out, the test line deleted, and the
expression definitions all reevaluated.

One way to do this might reasonably seem to be to define a typical set
of _numerical_ test values  a1, b1, . . .   and apply them as follows:

testValues = {a->a1, b->b1, . . . }

expr1 := . . .
expr2 := . . .
expr2  /.  testValues
expr3 := . . .
. . .

after which you remove the test line and re-evaluate all the
definitions.  But this approach apparently can encounter problems
arising from the order of evaluations.  So, how about

testValues = {a=a1, b=b1, . . . }

expr1 := . . .
expr2 := . . .
With[ testValues, expr2 ]
expr3 := . . .
. . .

Is that a safe approach to this objective?

```

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