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#### 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

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 { };

```

#### ERRORSDUETODIVISIONBYZEROORLOGARITHMOFZERO

```       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.

```

#### ERRORSDUETOINDIGESTIBLEARGUMENTS

```       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

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.

```

#### SEEALSO

```       Math::Trig

```

#### AUTHORS

```       Daniel S. Lewart <lewart!at!uiuc.edu> Jarkko Hietaniemi <jhi!at!iki.fi> Raphael Manfredi
<Raphael_Manfredi!at!pobox.com>

```

```       This library is free software; you can redistribute it and/or modify it under the same