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Math::BigFloat(3)
NAME
Math::BigFloat - Arbitrary size floating point math package
SYNOPSIS
use Math::BigFloat;
# Number creation
$x = Math::BigFloat->new($str); # defaults to 0
$nan = Math::BigFloat->bnan(); # create a NotANumber
$zero = Math::BigFloat->bzero(); # create a +0
$inf = Math::BigFloat->binf(); # create a +inf
$inf = Math::BigFloat->binf('-'); # create a -inf
$one = Math::BigFloat->bone(); # create a +1
$one = Math::BigFloat->bone('-'); # create a -1
# Testing
$x->is_zero(); # true if arg is +0
$x->is_nan(); # true if arg is NaN
$x->is_one(); # true if arg is +1
$x->is_one('-'); # true if arg is -1
$x->is_odd(); # true if odd, false for even
$x->is_even(); # true if even, false for odd
$x->is_positive(); # true if >= 0
$x->is_negative(); # true if < 0
$x->is_inf(sign); # true if +inf, or -inf (default is '+')
$x->bcmp($y); # compare numbers (undef,<0,=0,>0)
$x->bacmp($y); # compare absolutely (undef,<0,=0,>0)
$x->sign(); # return the sign, either +,- or NaN
$x->digit($n); # return the nth digit, counting from right
$x->digit(-$n); # return the nth digit, counting from left
# The following all modify their first argument. If you want to preserve
# $x, use $z = $x->copy()->bXXX($y); See under L<CAVEATS> for why this is
# neccessary when mixing $a = $b assigments with non-overloaded math.
# set
$x->bzero(); # set $i to 0
$x->bnan(); # set $i to NaN
$x->bone(); # set $x to +1
$x->bone('-'); # set $x to -1
$x->binf(); # set $x to inf
$x->binf('-'); # set $x to -inf
$x->bneg(); # negation
$x->babs(); # absolute value
$x->bnorm(); # normalize (no-op)
$x->bnot(); # two's complement (bit wise not)
$x->binc(); # increment x by 1
$x->bdec(); # decrement x by 1
$x->badd($y); # addition (add $y to $x)
$x->bsub($y); # subtraction (subtract $y from $x)
$x->bmul($y); # multiplication (multiply $x by $y)
$x->bdiv($y); # divide, set $x to quotient
# return (quo,rem) or quo if scalar
$x->bmod($y); # modulus ($x % $y)
$x->bpow($y); # power of arguments ($x ** $y)
$x->blsft($y); # left shift
$x->brsft($y); # right shift
# return (quo,rem) or quo if scalar
$x->blog(); # logarithm of $x to base e (Euler's number)
$x->blog($base); # logarithm of $x to base $base (f.i. 2)
$x->band($y); # bit-wise and
$x->bior($y); # bit-wise inclusive or
$x->bxor($y); # bit-wise exclusive or
$x->bnot(); # bit-wise not (two's complement)
$x->bsqrt(); # calculate square-root
$x->broot($y); # $y'th root of $x (e.g. $y == 3 => cubic root)
$x->bfac(); # factorial of $x (1*2*3*4*..$x)
$x->bround($N); # accuracy: preserve $N digits
$x->bfround($N); # precision: round to the $Nth digit
$x->bfloor(); # return integer less or equal than $x
$x->bceil(); # return integer greater or equal than $x
# The following do not modify their arguments:
bgcd(@values); # greatest common divisor
blcm(@values); # lowest common multiplicator
$x->bstr(); # return string
$x->bsstr(); # return string in scientific notation
$x->exponent(); # return exponent as BigInt
$x->mantissa(); # return mantissa as BigInt
$x->parts(); # return (mantissa,exponent) as BigInt
$x->length(); # number of digits (w/o sign and '.')
($l,$f) = $x->length(); # number of digits, and length of fraction
$x->precision(); # return P of $x (or global, if P of $x undef)
$x->precision($n); # set P of $x to $n
$x->accuracy(); # return A of $x (or global, if A of $x undef)
$x->accuracy($n); # set A $x to $n
# these get/set the appropriate global value for all BigFloat objects
Math::BigFloat->precision(); # Precision
Math::BigFloat->accuracy(); # Accuracy
Math::BigFloat->round_mode(); # rounding mode
DESCRIPTION
All operators (inlcuding basic math operations) are overloaded if you
declare your big floating point numbers as
$i = new Math::BigFloat '12_3.456_789_123_456_789E-2';
Operations with overloaded operators preserve the arguments, which is
exactly what you expect.
Canonical notation
Input to these routines are either BigFloat objects, or strings of the
following four forms:
· "/^[+-]\d+$/"
· "/^[+-]\d+\.\d*$/"
· "/^[+-]\d+E[+-]?\d+$/"
· "/^[+-]\d*\.\d+E[+-]?\d+$/"
all with optional leading and trailing zeros and/or spaces. Additonally,
numbers are allowed to have an underscore between any two digits.
Empty strings as well as other illegal numbers results in 'NaN'.
bnorm() on a BigFloat object is now effectively a no-op, since the numbers
are always stored in normalized form. On a string, it creates a BigFloat
object.
Output
Output values are BigFloat objects (normalized), except for bstr() and
bsstr().
The string output will always have leading and trailing zeros stripped and
drop a plus sign. "bstr()" will give you always the form with a decimal
point, while "bsstr()" (s for scientific) gives you the scientific
notation.
Input bstr() bsstr()
'-0' '0' '0E1'
' -123 123 123' '-123123123' '-123123123E0'
'00.0123' '0.0123' '123E-4'
'123.45E-2' '1.2345' '12345E-4'
'10E+3' '10000' '1E4'
Some routines ("is_odd()", "is_even()", "is_zero()", "is_one()",
"is_nan()") return true or false, while others ("bcmp()", "bacmp()") return
either undef, <0, 0 or >0 and are suited for sort.
Actual math is done by using the class defined with "with =" Class;> (which
defaults to BigInts) to represent the mantissa and exponent.
The sign "/^[+-]$/" is stored separately. The string 'NaN' is used to
represent the result when input arguments are not numbers, as well as the
result of dividing by zero.
"mantissa()", "exponent()" and "parts()"
"mantissa()" and "exponent()" return the said parts of the BigFloat as
BigInts such that:
$m = $x->mantissa();
$e = $x->exponent();
$y = $m * ( 10 ** $e );
print "ok\n" if $x == $y;
"($m,$e) = $x->parts();" is just a shortcut giving you both of them.
A zero is represented and returned as 0E1, not 0E0 (after Knuth).
Currently the mantissa is reduced as much as possible, favouring higher
exponents over lower ones (e.g. returning 1e7 instead of 10e6 or
10000000e0). This might change in the future, so do not depend on it.
Accuracy vs. Precision
See also: Rounding.
Math::BigFloat supports both precision and accuracy. For a full
documentation, examples and tips on these topics please see the large
section in Math::BigInt.
Since things like sqrt(2) or 1/3 must presented with a limited precision
lest a operation consumes all resources, each operation produces no more
than the requested number of digits.
Please refer to BigInt's documentation for the precedence rules of which
accuracy/precision setting will be used.
If there is no gloabl precision set, and the operation inquestion was not
called with a requested precision or accuracy, and the input $x has no
accuracy or precision set, then a fallback parameter will be used. For
historical reasons, it is called "div_scale" and can be accessed via:
$d = Math::BigFloat->div_scale(); # query
Math::BigFloat->div_scale($n); # set to $n digits
The default value is 40 digits.
In case the result of one operation has more precision than specified, it
is rounded. The rounding mode taken is either the default mode, or the one
supplied to the operation after the scale:
$x = Math::BigFloat->new(2);
Math::BigFloat->precision(5); # 5 digits max
$y = $x->copy()->bdiv(3); # will give 0.66666
$y = $x->copy()->bdiv(3,6); # will give 0.666666
$y = $x->copy()->bdiv(3,6,'odd'); # will give 0.666667
Math::BigFloat->round_mode('zero');
$y = $x->copy()->bdiv(3,6); # will give 0.666666
Rounding
ffround ( +$scale )
Rounds to the $scale'th place left from the '.', counting from the dot.
The first digit is numbered 1.
ffround ( -$scale )
Rounds to the $scale'th place right from the '.', counting from the dot.
ffround ( 0 )
Rounds to an integer.
fround ( +$scale )
Preserves accuracy to $scale digits from the left (aka significant
digits) and pads the rest with zeros. If the number is between 1 and -1,
the significant digits count from the first non-zero after the '.'
fround ( -$scale ) and fround ( 0 )
These are effectively no-ops.
All rounding functions take as a second parameter a rounding mode from one
of the following: 'even', 'odd', '+inf', '-inf', 'zero' or 'trunc'.
The default rounding mode is 'even'. By using
"Math::BigFloat->round_mode($round_mode);" you can get and set the default
mode for subsequent rounding. The usage of "$Math::BigFloat::$round_mode"
is no longer supported. The second parameter to the round functions then
overrides the default temporarily.
The "as_number()" function returns a BigInt from a Math::BigFloat. It uses
'trunc' as rounding mode to make it equivalent to:
$x = 2.5;
$y = int($x) + 2;
You can override this by passing the desired rounding mode as parameter to
"as_number()":
$x = Math::BigFloat->new(2.5);
$y = $x->as_number('odd'); # $y = 3
EXAMPLES
# not ready yet
Autocreating constants
After "use Math::BigFloat ':constant'" all the floating point constants in
the given scope are converted to "Math::BigFloat". This conversion happens
at compile time.
In particular
perl -MMath::BigFloat=:constant -e 'print 2E-100,"\n"'
prints the value of "2E-100". Note that without conversion of constants the
expression 2E-100 will be calculated as normal floating point number.
Please note that ':constant' does not affect integer constants, nor binary
nor hexadecimal constants. Use bignum or Math::BigInt to get this to work.
Math library
Math with the numbers is done (by default) by a module called
Math::BigInt::Calc. This is equivalent to saying:
use Math::BigFloat lib => 'Calc';
You can change this by using:
use Math::BigFloat lib => 'BitVect';
The following would first try to find Math::BigInt::Foo, then
Math::BigInt::Bar, and when this also fails, revert to Math::BigInt::Calc:
use Math::BigFloat lib => 'Foo,Math::BigInt::Bar';
Calc.pm uses as internal format an array of elements of some decimal base
(usually 1e7, but this might be differen for some systems) with the least
significant digit first, while BitVect.pm uses a bit vector of base 2, most
significant bit first. Other modules might use even different means of
representing the numbers. See the respective module documentation for
further details.
Please note that Math::BigFloat does not use the denoted library itself,
but it merely passes the lib argument to Math::BigInt. So, instead of the
need to do:
use Math::BigInt lib => 'GMP';
use Math::BigFloat;
you can roll it all into one line:
use Math::BigFloat lib => 'GMP';
It is also possible to just require Math::BigFloat:
require Math::BigFloat;
This will load the neccessary things (like BigInt) when they are needed,
and automatically.
Use the lib, Luke! And see "Using Math::BigInt::Lite" for more details than
you ever wanted to know about loading a different library.
Using Math::BigInt::Lite
It is possible to use Math::BigInt::Lite with Math::BigFloat:
# 1
use Math::BigFloat with => 'Math::BigInt::Lite';
There is no need to "use Math::BigInt" or "use Math::BigInt::Lite", but you
can combine these if you want. For instance, you may want to use
Math::BigInt objects in your main script, too.
# 2
use Math::BigInt;
use Math::BigFloat with => 'Math::BigInt::Lite';
Of course, you can combine this with the "lib" parameter.
# 3
use Math::BigFloat with => 'Math::BigInt::Lite', lib => 'GMP,Pari';
There is no need for a "use Math::BigInt;" statement, even if you want to
use Math::BigInt's, since Math::BigFloat will needs Math::BigInt and thus
always loads it. But if you add it, add it before:
# 4
use Math::BigInt;
use Math::BigFloat with => 'Math::BigInt::Lite', lib => 'GMP,Pari';
Notice that the module with the last "lib" will "win" and thus it's lib
will be used if the lib is available:
# 5
use Math::BigInt lib => 'Bar,Baz';
use Math::BigFloat with => 'Math::BigInt::Lite', lib => 'Foo';
That would try to load Foo, Bar, Baz and Calc (in that order). Or in other
words, Math::BigFloat will try to retain previously loaded libs when you
don't specify it onem but if you specify one, it will try to load them.
Actually, the lib loading order would be "Bar,Baz,Calc", and then
"Foo,Bar,Baz,Calc", but independend of which lib exists, the result is the
same as trying the latter load alone, except for the fact that one of Bar
or Baz might be loaded needlessly in an intermidiate step (and thus hang
around and waste memory). If neither Bar nor Baz exist (or don't
work/compile), they will still be tried to be loaded, but this is not as
time/memory consuming as actually loading one of them. Still, this type of
usage is not recommended due to these issues.
The old way (loading the lib only in BigInt) still works though:
# 6
use Math::BigInt lib => 'Bar,Baz';
use Math::BigFloat;
You can even load Math::BigInt afterwards:
# 7
use Math::BigFloat;
use Math::BigInt lib => 'Bar,Baz';
But this has the same problems like #5, it will first load Calc
(Math::BigFloat needs Math::BigInt and thus loads it) and then later Bar or
Baz, depending on which of them works and is usable/loadable. Since this
loads Calc unnecc., it is not recommended.
Since it also possible to just require Math::BigFloat, this poses the
question about what libary this will use:
require Math::BigFloat;
my $x = Math::BigFloat->new(123); $x += 123;
It will use Calc. Please note that the call to import() is still done, but
only when you use for the first time some Math::BigFloat math (it is
triggered via any constructor, so the first time you create a
Math::BigFloat, the load will happen in the background). This means:
require Math::BigFloat;
Math::BigFloat->import ( lib => 'Foo,Bar' );
would be the same as:
use Math::BigFloat lib => 'Foo, Bar';
But don't try to be clever to insert some operations in between:
require Math::BigFloat;
my $x = Math::BigFloat->bone() + 4; # load BigInt and Calc
Math::BigFloat->import( lib => 'Pari' ); # load Pari, too
$x = Math::BigFloat->bone()+4; # now use Pari
While this works, it loads Calc needlessly. But maybe you just wanted that?
Examples #3 is highly recommended for daily usage.
BUGS
Please see the file BUGS in the CPAN distribution Math::BigInt for known
bugs.
CAVEATS
stringify, bstr()
Both stringify and bstr() now drop the leading '+'. The old code would
return '+1.23', the new returns '1.23'. See the documentation in
Math::BigInt for reasoning and details.
bdiv
The following will probably not do what you expect:
print $c->bdiv(123.456),"\n";
It prints both quotient and reminder since print works in list context.
Also, bdiv() will modify $c, so be carefull. You probably want to use
print $c / 123.456,"\n";
print scalar $c->bdiv(123.456),"\n"; # or if you want to modify $c
instead.
Modifying and =
Beware of:
$x = Math::BigFloat->new(5);
$y = $x;
It will not do what you think, e.g. making a copy of $x. Instead it just
makes a second reference to the same object and stores it in $y. Thus
anything that modifies $x will modify $y (except overloaded math
operators), and vice versa. See Math::BigInt for details and how to avoid
that.
bpow
"bpow()" now modifies the first argument, unlike the old code which left
it alone and only returned the result. This is to be consistent with
"badd()" etc. The first will modify $x, the second one won't:
print bpow($x,$i),"\n"; # modify $x
print $x->bpow($i),"\n"; # ditto
print $x ** $i,"\n"; # leave $x alone
SEE ALSO
Math::BigInt, Math::BigRat and Math::Big as well as Math::BigInt::BitVect,
Math::BigInt::Pari and Math::BigInt::GMP.
The pragmas bignum, bigint and bigrat might also be of interest because
they solve the autoupgrading/downgrading issue, at least partly.
The package at
<http://search.cpan.org/search?mode=module&query=Math%3A%3ABigInt> contains
more documentation including a full version history, testcases, empty
subclass files and benchmarks.
LICENSE
This program is free software; you may redistribute it and/or modify it
under the same terms as Perl itself.
AUTHORS
Mark Biggar, overloaded interface by Ilya Zakharevich. Completely
rewritten by Tels http://bloodgate.com in 2001, 2002, and still at it in
2003.
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