Math::Complex(3pm) Perl Programmers Reference Guide Math::Complex(3pm)
NAME
Math::Complex - complex numbers and associated mathematical functions
SYNOPSIS
use Math::Complex;
$z = Math::Complex->make(5, 6);
$t = 4 - 3*i + $z;
$j = cplxe(1, 2*pi/3);
DESCRIPTION
This package lets you create and manipulate complex numbers. By
default, Perl limits itself to real numbers, but an extra "use"
statement brings full complex support, along with a full set of
mathematical functions typically associated with and/or extended to
complex numbers.
If you wonder what complex numbers are, they were invented to be able
to solve the following equation:
x*x = -1
and by definition, the solution is noted i (engineers use j instead
since i usually denotes an intensity, but the name does not matter).
The number i is a pure imaginary number.
The arithmetics with pure imaginary numbers works just like you would
expect it with real numbers... you just have to remember that
i*i = -1
so you have:
5i + 7i = i * (5 + 7) = 12i
4i - 3i = i * (4 - 3) = i
4i * 2i = -8
6i / 2i = 3
1 / i = -i
Complex numbers are numbers that have both a real part and an imaginary
part, and are usually noted:
a + bi
where "a" is the real part and "b" is the imaginary part. The
arithmetic with complex numbers is straightforward. You have to keep
track of the real and the imaginary parts, but otherwise the rules used
for real numbers just apply:
(4 + 3i) + (5 - 2i) = (4 + 5) + i(3 - 2) = 9 + i
(2 + i) * (4 - i) = 2*4 + 4i -2i -i*i = 8 + 2i + 1 = 9 + 2i
A graphical representation of complex numbers is possible in a plane
(also called the complex plane, but it's really a 2D plane). The
number
z = a + bi
is the point whose coordinates are (a, b). Actually, it would be the
vector originating from (0, 0) to (a, b). It follows that the addition
of two complex numbers is a vectorial addition.
Since there is a bijection between a point in the 2D plane and a
complex number (i.e. the mapping is unique and reciprocal), a complex
number can also be uniquely identified with polar coordinates:
[rho, theta]
where "rho" is the distance to the origin, and "theta" the angle
between the vector and the x axis. There is a notation for this using
the exponential form, which is:
rho * exp(i * theta)
where i is the famous imaginary number introduced above. Conversion
between this form and the cartesian form "a + bi" is immediate:
a = rho * cos(theta)
b = rho * sin(theta)
which is also expressed by this formula:
z = rho * exp(i * theta) = rho * (cos theta + i * sin theta)
In other words, it's the projection of the vector onto the x and y
axes. Mathematicians call rho the norm or modulus and theta the
argument of the complex number. The norm of "z" is marked here as
abs(z).
The polar notation (also known as the trigonometric representation) is
much more handy for performing multiplications and divisions of complex
numbers, whilst the cartesian notation is better suited for additions
and subtractions. Real numbers are on the x axis, and therefore y or
theta is zero or pi.
All the common operations that can be performed on a real number have
been defined to work on complex numbers as well, and are merely
extensions of the operations defined on real numbers. This means they
keep their natural meaning when there is no imaginary part, provided
the number is within their definition set.
For instance, the "sqrt" routine which computes the square root of its
argument is only defined for non-negative real numbers and yields a
non-negative real number (it is an application from R+ to R+). If we
allow it to return a complex number, then it can be extended to
negative real numbers to become an application from R to C (the set of
complex numbers):
sqrt(x) = x >= 0 ? sqrt(x) : sqrt(-x)*i
It can also be extended to be an application from C to C, whilst its
restriction to R behaves as defined above by using the following
definition:
sqrt(z = [r,t]) = sqrt(r) * exp(i * t/2)
Indeed, a negative real number can be noted "[x,pi]" (the modulus x is
always non-negative, so "[x,pi]" is really "-x", a negative number) and
the above definition states that
sqrt([x,pi]) = sqrt(x) * exp(i*pi/2) = [sqrt(x),pi/2] = sqrt(x)*i
which is exactly what we had defined for negative real numbers above.
The "sqrt" returns only one of the solutions: if you want the both, use
the "root" function.
All the common mathematical functions defined on real numbers that are
extended to complex numbers share that same property of working as
usual when the imaginary part is zero (otherwise, it would not be
called an extension, would it?).
A new operation possible on a complex number that is the identity for
real numbers is called the conjugate, and is noted with a horizontal
bar above the number, or "~z" here.
z = a + bi
~z = a - bi
Simple... Now look:
z * ~z = (a + bi) * (a - bi) = a*a + b*b
We saw that the norm of "z" was noted abs(z) and was defined as the
distance to the origin, also known as:
rho = abs(z) = sqrt(a*a + b*b)
so
z * ~z = abs(z) ** 2
If z is a pure real number (i.e. "b == 0"), then the above yields:
a * a = abs(a) ** 2
which is true ("abs" has the regular meaning for real number, i.e.
stands for the absolute value). This example explains why the norm of
"z" is noted abs(z): it extends the "abs" function to complex numbers,
yet is the regular "abs" we know when the complex number actually has
no imaginary part... This justifies a posteriori our use of the "abs"
notation for the norm.
OPERATIONS
Given the following notations:
z1 = a + bi = r1 * exp(i * t1)
z2 = c + di = r2 * exp(i * t2)
z = <any complex or real number>
the following (overloaded) operations are supported on complex numbers:
z1 + z2 = (a + c) + i(b + d)
z1 - z2 = (a - c) + i(b - d)
z1 * z2 = (r1 * r2) * exp(i * (t1 + t2))
z1 / z2 = (r1 / r2) * exp(i * (t1 - t2))
z1 ** z2 = exp(z2 * log z1)
~z = a - bi
abs(z) = r1 = sqrt(a*a + b*b)
sqrt(z) = sqrt(r1) * exp(i * t/2)
exp(z) = exp(a) * exp(i * b)
log(z) = log(r1) + i*t
sin(z) = 1/2i (exp(i * z1) - exp(-i * z))
cos(z) = 1/2 (exp(i * z1) + exp(-i * z))
atan2(y, x) = atan(y / x) # Minding the right quadrant, note the order.
The definition used for complex arguments of atan2() is
-i log((x + iy)/sqrt(x*x+y*y))
Note that atan2(0, 0) is not well-defined.
The following extra operations are supported on both real and complex
numbers:
Re(z) = a
Im(z) = b
arg(z) = t
abs(z) = r
cbrt(z) = z ** (1/3)
log10(z) = log(z) / log(10)
logn(z, n) = log(z) / log(n)
tan(z) = sin(z) / cos(z)
csc(z) = 1 / sin(z)
sec(z) = 1 / cos(z)
cot(z) = 1 / tan(z)
asin(z) = -i * log(i*z + sqrt(1-z*z))
acos(z) = -i * log(z + i*sqrt(1-z*z))
atan(z) = i/2 * log((i+z) / (i-z))
acsc(z) = asin(1 / z)
asec(z) = acos(1 / z)
acot(z) = atan(1 / z) = -i/2 * log((i+z) / (z-i))
sinh(z) = 1/2 (exp(z) - exp(-z))
cosh(z) = 1/2 (exp(z) + exp(-z))
tanh(z) = sinh(z) / cosh(z) = (exp(z) - exp(-z)) / (exp(z) + exp(-z))
csch(z) = 1 / sinh(z)
sech(z) = 1 / cosh(z)
coth(z) = 1 / tanh(z)
asinh(z) = log(z + sqrt(z*z+1))
acosh(z) = log(z + sqrt(z*z-1))
atanh(z) = 1/2 * log((1+z) / (1-z))
acsch(z) = asinh(1 / z)
asech(z) = acosh(1 / z)
acoth(z) = atanh(1 / z) = 1/2 * log((1+z) / (z-1))
arg, abs, log, csc, cot, acsc, acot, csch, coth, acosech, acotanh, have
aliases rho, theta, ln, cosec, cotan, acosec, acotan, cosech, cotanh,
acosech, acotanh, respectively. "Re", "Im", "arg", "abs", "rho", and
"theta" can be used also as mutators. The "cbrt" returns only one of
the solutions: if you want all three, use the "root" function.
The root function is available to compute all the n roots of some
complex, where n is a strictly positive integer. There are exactly n
such roots, returned as a list. Getting the number mathematicians call
"j" such that:
1 + j + j*j = 0;
is a simple matter of writing:
$j = ((root(1, 3))[1];
The kth root for "z = [r,t]" is given by:
(root(z, n))[k] = r**(1/n) * exp(i * (t + 2*k*pi)/n)
You can return the kth root directly by "root(z, n, k)", indexing
starting from zero and ending at n - 1.
The spaceship numeric comparison operator, <=>, is also defined. In
order to ensure its restriction to real numbers is conform to what you
would expect, the comparison is run on the real part of the complex
number first, and imaginary parts are compared only when the real parts
match.
CREATION
To create a complex number, use either:
$z = Math::Complex->make(3, 4);
$z = cplx(3, 4);
if you know the cartesian form of the number, or
$z = 3 + 4*i;
if you like. To create a number using the polar form, use either:
$z = Math::Complex->emake(5, pi/3);
$x = cplxe(5, pi/3);
instead. The first argument is the modulus, the second is the angle (in
radians, the full circle is 2*pi). (Mnemonic: "e" is used as a
notation for complex numbers in the polar form).
It is possible to write:
$x = cplxe(-3, pi/4);
but that will be silently converted into "[3,-3pi/4]", since the
modulus must be non-negative (it represents the distance to the origin
in the complex plane).
It is also possible to have a complex number as either argument of the
"make", "emake", "cplx", and "cplxe": the appropriate component of the
argument will be used.
$z1 = cplx(-2, 1);
$z2 = cplx($z1, 4);
The "new", "make", "emake", "cplx", and "cplxe" will also understand a
single (string) argument of the forms
2-3i
-3i
[2,3]
[2,-3pi/4]
[2]
in which case the appropriate cartesian and exponential components will
be parsed from the string and used to create new complex numbers. The
imaginary component and the theta, respectively, will default to zero.
The "new", "make", "emake", "cplx", and "cplxe" will also understand
the case of no arguments: this means plain zero or (0, 0).
DISPLAYING
When printed, a complex number is usually shown under its cartesian
style a+bi, but there are legitimate cases where the polar style [r,t]
is more appropriate. The process of converting the complex number into
a string that can be displayed is known as stringification.
By calling the class method "Math::Complex::display_format" and
supplying either "polar" or "cartesian" as an argument, you override
the default display style, which is "cartesian". Not supplying any
argument returns the current settings.
This default can be overridden on a per-number basis by calling the
"display_format" method instead. As before, not supplying any argument
returns the current display style for this number. Otherwise whatever
you specify will be the new display style for this particular number.
For instance:
use Math::Complex;
Math::Complex::display_format('polar');
$j = (root(1, 3))[1];
print "j = $j\n"; # Prints "j = [1,2pi/3]"
$j->display_format('cartesian');
print "j = $j\n"; # Prints "j = -0.5+0.866025403784439i"
The polar style attempts to emphasize arguments like k*pi/n (where n is
a positive integer and k an integer within [-9, +9]), this is called
polar pretty-printing.
For the reverse of stringifying, see the "make" and "emake".
CHANGED IN PERL 5.6
The "display_format" class method and the corresponding
"display_format" object method can now be called using a parameter hash
instead of just a one parameter.
The old display format style, which can have values "cartesian" or
"polar", can be changed using the "style" parameter.
$j->display_format(style => "polar");
The one parameter calling convention also still works.
$j->display_format("polar");
There are two new display parameters.
The first one is "format", which is a sprintf()-style format string to
be used for both numeric parts of the complex number(s). The is
somewhat system-dependent but most often it corresponds to "%.15g".
You can revert to the default by setting the "format" to "undef".
# the $j from the above example
$j->display_format('format' => '%.5f');
print "j = $j\n"; # Prints "j = -0.50000+0.86603i"
$j->display_format('format' => undef);
print "j = $j\n"; # Prints "j = -0.5+0.86603i"
Notice that this affects also the return values of the "display_format"
methods: in list context the whole parameter hash will be returned, as
opposed to only the style parameter value. This is a potential
incompatibility with earlier versions if you have been calling the
"display_format" method in list context.
The second new display parameter is "polar_pretty_print", which can be
set to true or false, the default being true. See the previous section
for what this means.
USAGE
Thanks to overloading, the handling of arithmetics with complex numbers
is simple and almost transparent.
Here are some examples:
use Math::Complex;
$j = cplxe(1, 2*pi/3); # $j ** 3 == 1
print "j = $j, j**3 = ", $j ** 3, "\n";
print "1 + j + j**2 = ", 1 + $j + $j**2, "\n";
$z = -16 + 0*i; # Force it to be a complex
print "sqrt($z) = ", sqrt($z), "\n";
$k = exp(i * 2*pi/3);
print "$j - $k = ", $j - $k, "\n";
$z->Re(3); # Re, Im, arg, abs,
$j->arg(2); # (the last two aka rho, theta)
# can be used also as mutators.
CONSTANTS
PI
The constant "pi" and some handy multiples of it (pi2, pi4, and pip2
(pi/2) and pip4 (pi/4)) are also available if separately exported:
use Math::Complex ':pi';
$third_of_circle = pi2 / 3;
Inf
The floating point infinity can be exported as a subroutine Inf():
use Math::Complex qw(Inf sinh);
my $AlsoInf = Inf() + 42;
my $AnotherInf = sinh(1e42);
print "$AlsoInf is $AnotherInf\n" if $AlsoInf == $AnotherInf;
Note that the stringified form of infinity varies between platforms: it
can be for example any of
inf
infinity
INF
1.#INF
or it can be something else.
Also note that in some platforms trying to use the infinity in
arithmetic operations may result in Perl crashing because using an
infinity causes SIGFPE or its moral equivalent to be sent. The way to
ignore this is
local $SIG{FPE} = sub { };
ERRORS DUE TO DIVISION BY ZERO OR LOGARITHM OF ZERO
The division (/) and the following functions
log ln log10 logn
tan sec csc cot
atan asec acsc acot
tanh sech csch coth
atanh asech acsch acoth
cannot be computed for all arguments because that would mean dividing
by zero or taking logarithm of zero. These situations cause fatal
runtime errors looking like this
cot(0): Division by zero.
(Because in the definition of cot(0), the divisor sin(0) is 0)
Died at ...
or
atanh(-1): Logarithm of zero.
Died at...
For the "csc", "cot", "asec", "acsc", "acot", "csch", "coth", "asech",
"acsch", the argument cannot be 0 (zero). For the logarithmic
functions and the "atanh", "acoth", the argument cannot be 1 (one).
For the "atanh", "acoth", the argument cannot be "-1" (minus one). For
the "atan", "acot", the argument cannot be "i" (the imaginary unit).
For the "atan", "acoth", the argument cannot be "-i" (the negative
imaginary unit). For the "tan", "sec", "tanh", the argument cannot be
pi/2 + k * pi, where k is any integer. atan2(0, 0) is undefined, and
if the complex arguments are used for atan2(), a division by zero will
happen if z1**2+z2**2 == 0.
Note that because we are operating on approximations of real numbers,
these errors can happen when merely `too close' to the singularities
listed above.
ERRORS DUE TO INDIGESTIBLE ARGUMENTS
The "make" and "emake" accept both real and complex arguments. When
they cannot recognize the arguments they will die with error messages
like the following
Math::Complex::make: Cannot take real part of ...
Math::Complex::make: Cannot take real part of ...
Math::Complex::emake: Cannot take rho of ...
Math::Complex::emake: Cannot take theta of ...
BUGS
Saying "use Math::Complex;" exports many mathematical routines in the
caller environment and even overrides some ("sqrt", "log", "atan2").
This is construed as a feature by the Authors, actually... ;-)
All routines expect to be given real or complex numbers. Don't attempt
to use BigFloat, since Perl has currently no rule to disambiguate a '+'
operation (for instance) between two overloaded entities.
In Cray UNICOS there is some strange numerical instability that results
in root(), cos(), sin(), cosh(), sinh(), losing accuracy fast. Beware.
The bug may be in UNICOS math libs, in UNICOS C compiler, in
Math::Complex. Whatever it is, it does not manifest itself anywhere
else where Perl runs.
SEE ALSO
Math::Trig
AUTHORS
Daniel S. Lewart <lewart!at!uiuc.edu>, Jarkko Hietaniemi
<jhi!at!iki.fi>, Raphael Manfredi <Raphael_Manfredi!at!pobox.com>,
Zefram <zefram AT fysh.org>
LICENSE
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.16.3 2013-03-04 Math::Complex(3pm)
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