calc: Variables
5.14 Variables
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A “variable” is somewhere between a storage register on a conventional
calculator, and a variable in a programming language. (In fact, a Calc
variable is really just an Emacs Lisp variable that contains a Calc
number or formula.) A variable’s name is normally composed of letters
and digits. Calc also allows apostrophes and ‘#’ signs in variable
names. (The Calc variable ‘foo’ corresponds to the Emacs Lisp variable
‘var-foo’, but unless you access the variable from within Emacs Lisp,
you don’t need to worry about it. Variable names in algebraic formulas
implicitly have ‘var-’ prefixed to their names. The ‘#’ character in
variable names used in algebraic formulas corresponds to a dash ‘-’ in
the Lisp variable name. If the name contains any dashes, the prefix
‘var-’ is _not_ automatically added. Thus the two formulas ‘foo + 1’
and ‘var#foo + 1’ both refer to the same variable.)
In a command that takes a variable name, you can either type the full
name of a variable, or type a single digit to use one of the special
convenience variables ‘q0’ through ‘q9’. For example, ‘3 s s 2’ stores
the number 3 in variable ‘q2’, and ‘3 s s foo <RET>’ stores that number
in variable ‘foo’.
To push a variable itself (as opposed to the variable’s value) on the
stack, enter its name as an algebraic expression using the apostrophe
(<'>) key.
The ‘=’ (‘calc-evaluate’) key “evaluates” a formula by replacing all
variables in the formula which have been given values by a ‘calc-store’
or ‘calc-let’ command by their stored values. Other variables are left
alone. Thus a variable that has not been stored acts like an abstract
variable in algebra; a variable that has been stored acts more like a
register in a traditional calculator. With a positive numeric prefix
argument, ‘=’ evaluates the top N stack entries; with a negative
argument, ‘=’ evaluates the Nth stack entry.
A few variables are called “special constants”. Their names are ‘e’,
‘pi’, ‘i’, ‘phi’, and ‘gamma’. (
Scientific Functions.) When
they are evaluated with ‘=’, their values are calculated if necessary
according to the current precision or complex polar mode. If you wish
to use these symbols for other purposes, simply undefine or redefine
them using ‘calc-store’.
The variables ‘inf’, ‘uinf’, and ‘nan’ stand for infinite or
indeterminate values. It’s best not to use them as regular variables,
since Calc uses special algebraic rules when it manipulates them. Calc
displays a warning message if you store a value into any of these
special variables.
Store and Recall, for a discussion of commands dealing with
variables.
Info Catalog
calc: Incomplete Objects
calc: Data Types
calc: Formulas