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Re: A kernel, multiple notebooks, and Global?

• To: mathgroup at smc.vnet.net
• Subject: [mg87738] Re: A kernel, multiple notebooks, and Global?
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Wed, 16 Apr 2008 05:05:50 -0400 (EDT)

On 4/15/08 at 5:51 AM, siegman at stanford.edu (AES) wrote:

>Pardon any awkward wordings here, but I may not have all the jargon
>relevant to my query clearly understood.

>Suppose that on a single-user computer I have several notebooks open
>that address different parts of a common calculation, and thus share
>overlapping sets of globally used variable names.

>The broad question is then, how far can I go -- or what dangers may
>lurk -- in treating these multiple notebooks as essentially one
>unified notebook that just happens to be stored in multiple files
>and appear on screen in multiple windows?

The only real issue here is your being able to keep track of
what is going on. That is I am confident, long before you run
out of resources (memory etc) you will have too many windows to
be convenient for your use.

>1)  For example, in terms of contexts or scopes, I'm guessing that
>"Global is Global":  the Global` context for all of these notebooks
>is set by or recorded by the kernel, and at any one instant is
>exactly the same for all these open notebooks  -- right?

Right.

>2)  Suppose a certain Input cell is present in exactly identical
>form at some random (i.e., different) point in each of the
>notebooks; I've been executing cells from all of the notebooks in
>some irregular sequence; and then I execute this particular cell in
>whichever of the notebooks happens to be most convenient for me.

Right. But you will need to be careful about dependencies in
each of the notebooks.

>I assume the kernel is likely to be able to recognize which notebook
>submitted these Input instructions.

I think this implies more tracking done by the kernel than is
the case. I believe the kernel simply sees every thing as a
sequence of operations and simply sends results back to which
ever notebook was the evaluation notebook at the time. That is,
I don't believe once you have evaluated several expressions in
several notebooks there is a means within Mathematica to find
the notebook containing say the 10th expression that was evaluated.

>But beyond that, unless this cell contains some code which directly or
>indirectly identifies the notebook in which the cell resides, and uses
>this information to modify the Input instructions, executing the copy
>of this cell that resides in any of the notebooks will produce exactly
>the same result, except for where it displays its output -- right?

Right. But watch out for unexpected dependencies. It is really
easy when working in this manner to miss a change in a variable
in one notebook that impacts another notebook.