Other Operations on Variables
=============================

The `s e' (`calc-edit-variable') command edits the stored value of a
variable without ever putting that value on the stack or simplifying
or evaluating the value.  It prompts for the name of the variable to
edit.  If the variable has no stored value, the editing buffer will
start out empty.  If the editing buffer is empty when you press M-#
M-# to finish, the variable will be made void.  *Note Editing Stack
Entries::, for a general description of editing.

The `s e' command is especially useful for creating and editing
rewrite rules which are stored in variables.  Sometimes these rules
contain formulas which must not be evaluated until the rules are
actually used.  (For example, they may refer to `deriv(x,y)', where
`x' will someday become some expression involving `y'; if you let Calc
evaluate the rule while you are defining it, Calc will replace
`deriv(x,y)' with 0 because the formula `x' does not itself refer to
`y'.)  By contrast, recalling the variable, editing with ``', and
storing will evaluate the variable's value as a side effect of putting
the value on the stack.

There are several special-purpose variable-editing commands that use
the `s' prefix followed by a shifted letter:

`s A'
     Edit `AlgSimpRules'.  See Algebraic Simplifications.
`s D'
     Edit `Decls'.  See Declarations.
`s E'
     Edit `EvalRules'.  See Default Simplifications.
`s F'
     Edit `FitRules'.  See Curve Fitting.
`s G'
     Edit `GenCount'.  See Solving Equations.
`s H'
     Edit `Holidays'.  See Business Days.
`s I'
     Edit `IntegLimit'.  See Calculus.
`s L'
     Edit `LineStyles'.  See Graphics.
`s P'
     Edit `PointStyles'.  See Graphics.
`s R'
     Edit `PlotRejects'.  See Graphics.
`s T'
     Edit `TimeZone'.  See Time Zones.
`s U'
     Edit `Units'.  See User-Defined Units.
`s X'
     Edit `ExtSimpRules'.  See Unsafe Simplifications.

These commands are just versions of `s e' that use fixed variable
names rather than prompting for the variable name.

The `s p' (`calc-permanent-variable') command saves a
variable's value permanently in your `.emacs' file, so that its
value will still be available in future Emacs sessions.  You can
re-execute `s p' later on to update the saved value, but the
only way to remove a saved variable is to edit your `.emacs' file
by hand.  (See General Mode Commands, for a way to tell Calc to
use a different file instead of `.emacs'.)

If you do not specify the name of a variable to save (i.e., `s p
RET'), all `var-' variables with defined values are saved except for
the special constants `pi', `e', `i', `phi', and `gamma'; the
variables `TimeZone' and `PlotRejects'; `FitRules', `DistribRules',
and other built-in rewrite rules; and `PlotDataN' variables generated
by the graphics commands.  (You can still save these variables by
explicitly naming them in an `s p' command.)

The `s i' (`calc-insert-variables') command writes
the values of all `var-' variables into a specified buffer.
The variables are written in the form of Lisp `setq' commands
which store the values in string form.  You can place these commands
in your `.emacs' buffer if you wish, though in this case it
would be easier to use `s p RET'.  (Note that `s i'
omits the same set of variables as `s p RET'; the difference
is that `s i' will store the variables in any buffer, and it also
stores in a more human-readable format.)