The `s s` (`calc-store`

) command stores the value at the top of
the stack into a specified variable. It prompts you to enter the
name of the variable. If you press a single digit, the value is stored
immediately in one of the "quick" variables `var-q0`

through
`var-q9`

. Or you can enter any variable name. The prefix ``var-'`
is supplied for you; when a name appears in a formula (as in ``a+q2'`)
the prefix ``var-'` is also supplied there, so normally you can simply
forget about ``var-'` everywhere. Its only purpose is to enable you to
use Calc variables without fear of accidentally clobbering some variable in
another Emacs package. If you really want to store in an arbitrary Lisp
variable, just backspace over the ``var-'`.

The `s s` command leaves the stored value on the stack. There is
also an `s t` (`calc-store-into`

) command, which removes a
value from the stack and stores it in a variable.

If the top of stack value is an equation ``a = 7'` or assignment
``a := 7'` with a variable on the lefthand side, then Calc will
assign that variable with that value by default, i.e., if you type
`s s RET` or

`b`

.)
In fact, the top of stack value can be a vector of equations or assignments with different variables on their lefthand sides; the default will be to store all the variables with their corresponding righthand sides simultaneously.

It is also possible to type an equation or assignment directly at
the prompt for the `s s` or `s t` command: `s s foo = 7`.
In this case the expression to the right of the `=` or `:=`
symbol is evaluated as if by the `=` command, and that value is
stored in the variable. No value is taken from the stack; `s s`
and `s t` are equivalent when used in this way.

The prefix keys `s` and `t` may be followed immediately by a
digit; `s 9` is equivalent to `s s 9`, and `t 9` is
equivalent to `s t 9`. (The `t` prefix is otherwise used
for trail and time/date commands.)

There are also several "arithmetic store" commands. For example,
`s +` removes a value from the stack and adds it to the specified
variable. The other arithmetic stores are `s -`, `s *`, `s /`,
`s ^`, and `s |` (vector concatenation), plus `s n` and
`s &` which negate or invert the value in a variable, and `s [`
and `s ]` which decrease or increase a variable by one.

All the arithmetic stores accept the Inverse prefix to reverse the
order of the operands. If v represents the contents of the
variable, and a is the value drawn from the stack, then regular
`s -` assigns @c{$v \coloneq v - a$}
v := v - a, but `I s -` assigns
v := a - v. While `I s *` might seem pointless, it is
useful if matrix multiplication is involved. Actually, all the
arithmetic stores use formulas designed to behave usefully both
forwards and backwards:

s + v := v + a v := a + v s - v := v - a v := a - v s * v := v * a v := a * v s / v := v / a v := a / v s ^ v := v ^ a v := a ^ v s | v := v | a v := a | v s n v := v / (-1) v := (-1) / v s & v := v ^ (-1) v := (-1) ^ v s [ v := v - 1 v := 1 - v s ] v := v - (-1) v := (-1) - v

In the last four cases, a numeric prefix argument will be used in
place of the number one. (For example, `M-2 s ]` increases
a variable by 2, and `M-2 I s ]` replaces a variable by
minus-two minus the variable.

The first six arithmetic stores can also be typed `s t +`, `s t -`,
etc. The commands `s s +`, `s s -`, and so on are analogous
arithmetic stores that don't remove the value a from the stack.

All arithmetic stores report the new value of the variable in the
Trail for your information. They signal an error if the variable
previously had no stored value. If default simplifications have been
turned off, the arithmetic stores temporarily turn them on for numeric
arguments only (i.e., they temporarily do an `m N` command).
See section Simplification Modes. Large vectors put in the trail by
these commands always use abbreviated (`t .`) mode.

The `s m` command is a general way to adjust a variable's value
using any Calc function. It is a "mapping" command analogous to
`V M`, `V R`, etc. See section Reducing and Mapping Vectors, to see
how to specify a function for a mapping command. Basically,
all you do is type the Calc command key that would invoke that
function normally. For example, `s m n` applies the `n`
key to negate the contents of the variable, so `s m n` is
equivalent to `s n`. Also, `s m Q` takes the square root
of the value stored in a variable, `s m v v` uses `v v` to
reverse the vector stored in the variable, and `s m H I S`
takes the hyperbolic arcsine of the variable contents.

If the mapping function takes two or more arguments, the additional
arguments are taken from the stack; the old value of the variable
is provided as the first argument. Thus `s m -` with a
on the stack computes v - a, just like `s -`. With the
Inverse prefix, the variable's original value becomes the *last*
argument instead of the first. Thus `I s m -` is also
equivalent to `I s -`.

The `s x` (`calc-store-exchange`

) command exchanges the value
of a variable with the value on the top of the stack. Naturally, the
variable must already have a stored value for this to work.

You can type an equation or assignment at the `s x` prompt. The
command `s x a=6` takes no values from the stack; instead, it
pushes the old value of ``a'` on the stack and stores ``a = 6'`.

Until you store something in them, variables are "void," that is, they
contain no value at all. If they appear in an algebraic formula they
will be left alone even if you press `=` (`calc-evaluate`

).
The `s u` (`calc-unstore`

) command returns a variable to the
void state.

The only variables with predefined values are the "special constants"
`pi`

, `e`

, `i`

, `phi`

, and `gamma`

. You are free
to unstore these variables or to store new values into them if you like,
although some of the algebraic-manipulation functions may assume these
variables represent their standard values. Calc displays a warning if
you change the value of one of these variables, or of one of the other
special variables `inf`

, `uinf`

, and `nan`

(which are
normally void).

Note that `var-pi`

doesn't actually have 3.14159265359 stored
in it, but rather a special magic value that evaluates to @c{$\pi$}
pi
at the current precision. Likewise `var-e`

, `var-i`

, and
`var-phi`

evaluate according to the current precision or polar mode.
If you recall a value from `pi`

and store it back, this magic
property will be lost.

The `s c` (`calc-copy-variable`

) command copies the stored
value of one variable to another. It differs from a simple `s r`
followed by an `s t` in two important ways. First, the value never
goes on the stack and thus is never rounded, evaluated, or simplified
in any way; it is not even rounded down to the current precision.
Second, the "magic" contents of a variable like `var-e`

can
be copied into another variable with this command, perhaps because
you need to unstore `var-e`

right now but you wish to put it
back when you're done. The `s c` command is the only way to
manipulate these magic values intact.

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