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A floating-point number or *float* is a number stored in scientific
notation. The number of significant digits in the fractional part is
governed by the current floating precision (see Precision). The
range of acceptable values is from
‘`10^-3999999`’
(inclusive) to
‘`10^4000000`’
(exclusive), plus the corresponding negative values and zero.

Calculations that would exceed the allowable range of values (such
as ‘`exp(exp(20))`’) are left in symbolic form by Calc. The
messages “floating-point overflow” or “floating-point underflow”
indicate that during the calculation a number would have been produced
that was too large or too close to zero, respectively, to be represented
by Calc. This does not necessarily mean the final result would have
overflowed, just that an overflow occurred while computing the result.
(In fact, it could report an underflow even though the final result
would have overflowed!)

If a rational number and a float are mixed in a calculation, the result
will in general be expressed as a float. Commands that require an integer
value (such as `k g` [`gcd`

]) will also accept integer-valued
floats, i.e., floating-point numbers with nothing after the decimal point.

Floats are identified by the presence of a decimal point and/or an
exponent. In general a float consists of an optional sign, digits
including an optional decimal point, and an optional exponent consisting
of an ‘`e`’, an optional sign, and up to seven exponent digits.
For example, ‘`23.5e-2`’ is 23.5 times ten to the minus-second power,
or 0.235.

Floating-point numbers are normally displayed in decimal notation with all significant figures shown. Exceedingly large or small numbers are displayed in scientific notation. Various other display options are available. See Float Formats.

Floating-point numbers are stored in decimal, not binary. The result of each operation is rounded to the nearest value representable in the number of significant digits specified by the current precision, rounding away from zero in the case of a tie. Thus (in the default display mode) what you see is exactly what you get. Some operations such as square roots and transcendental functions are performed with several digits of extra precision and then rounded down, in an effort to make the final result accurate to the full requested precision. However, accuracy is not rigorously guaranteed. If you suspect the validity of a result, try doing the same calculation in a higher precision. The Calculator’s arithmetic is not intended to be IEEE-conformant in any way.

While floats are always *stored* in decimal, they can be entered
and displayed in any radix just like integers and fractions. Since a
float that is entered in a radix other that 10 will be converted to
decimal, the number that Calc stores may not be exactly the number that
was entered, it will be the closest decimal approximation given the
current precision. The notation ‘` radix#ddd.ddd`’
is a floating-point number whose digits are in the specified radix.
Note that the ‘

Next: Complex Numbers, Previous: Fractions, Up: Data Types [Contents][Index]