Rectangular form of a complex expression
This functionality does not run in MATLAB.
rectform(z
)
rectform(z)
computes the rectangular form
of the complex expression z,
i.e., it splits z into z = ℜ(z)
+ i ℑ(z).
rectform(z)
tries to split z
into
its real and imaginary part and to return z
in
the form z = ℜ(z)
+ i ℑ(z).
rectform
works recursively, i.e., it first
tries to split each subexpression of z
into its
real and imaginary part and then tackles z
as a
whole.
Use Re
and Im
to extract
the real and imaginary parts, respectively, from the result of rectform
.
See Example 1.
rectform
is more powerful than a direct application
of Re
and Im
to z
.
However, usually it is much slower. For constant arithmetical expressions,
it is therefore recommended to use the functions Re
and Im
directly.
See Example 2.
The main use of rectform
is for symbolic
expressions, and properties of
identifiers are taken into account (see assume
). An identifier without any property
is assumed to be complex valued. See Example 3.
If z
is an array,
a list, or a set,
then rectform
is applied to each entry of z
.
If z
is an hfarray,
then rectform
returns z
unchanged.
If z
is a polynomial or a series expansion, of type Series::Puiseux
or Series::gseries
, then rectform
is
applied to each coefficient of z
.
See Example 5.
The result r := rectform(z)
is an element
of the domain rectform
.
Such a domain
element consists of three operands, satisfying the following
equality: z = op(r, 1) + I*op(r, 2) + op(r, 3)
.
The first two operands are real arithmetical expressions, and the
third operand is an expression that cannot be split into its real
and imaginary part.
Sometimes rectform
is unable to compute the
required decomposition. Then it still tries to return some partial
information by extracting as much as possible from the real and imaginary
part of z
. The extracted parts are stored in the
first two operands, and the third operand contains the remainder,
where no further extraction is possible. In extreme cases, the first
two operands may even be zero. Example 6 illustrates
some possible cases.
Arithmetical operations with elements of the domain type rectform
are
possible. The result of an arithmetical operation is again an element
of this domain (see Example 4).
Most MuPAD^{®} functions handling arithmetical expressions (e.g., expand
, normal
, simplify
etc.) can be
applied to elements of type rectform
. They act
on each of the three operands individually.
Use expr
to
convert the result of rectform
into an element
of a basic
domain. See Example 4.
The function is sensitive to properties of
identifiers set via assume
.
See Example 3.
The rectangular form of sin(z) for complex values z is:
delete z: r := rectform(sin(z))
The real and the imaginary part can be extracted as follows:
Re(r), Im(r)
The complex conjugate of r
can be obtained
directly:
conjugate(r)
The real and the imaginary part of a constant arithmetical expression
can be determined by the functions Re
and Im
, as in the following example:
Re(ln(4)) + I*Im(ln(4))
In fact, they work much faster than rectform
.
However, they fail to compute the real and the imaginary part of arbitrary
symbolic expressions, such as for the term e^{i sin(z)}:
delete z: f := exp(I*sin(z)): Re(f), Im(f)
The function rectform
is more powerful. It
is able to split the expression above into its real and imaginary
part:
r := rectform(f)
Now we can extract the real and the imaginary part of f
:
Re(r)
Im(r)
Identifiers without properties are considered to be complex variables:
delete z: rectform(ln(z))
However, you can affect the behavior of rectform
by
attaching properties to the identifiers. For example, if z assumes
only real negative values, the real and the imaginary part simplify
considerably:
assume(z < 0): rectform(ln(z))
We compute the rectangular form of the complex variable x:
delete x: a := rectform(x)
Then we do the same for the real variable y:
delete y: assume(y, Type::Real): b := rectform(y)
domtype(a), domtype(b)
We have stored the results, i.e., the elements of domain type rectform
,
in the two identifiers a
and b
.
We compute the sum of a
and b
,
which is again of domain type rectform
, i.e., it
is already splitted into its real and imaginary part:
c := a + b
domtype(c)
The result of an arithmetical operation between an element of
domain type rectform
and an arbitrary arithmetical
expression is of domain type rectform
as well:
delete z: d := a + 2*b + exp(z)
domtype(d)
Use the function expr
to
convert an element of domain type rectform
into
an element of a basic domain:
expr(d)
domtype(%)
rectform
also works for polynomials and series expansions, namely
individually on each coefficient:
delete x, y: p := poly(ln(4) + y*x, [x]): rectform(p)
Similarly, rectform
works for lists, sets,
or arrays, where it is applied to each
individual entry:
a := array(1..2, [x, y]): rectform(a)
hfarrays are returned unchanged:
a := hfarray(1..2, [1.0, 2.0]): rectform(a)
Note that rectform
does not work directly
for other basic data types. For example, if the input expression is
a table of arithmetical expressions,
then rectform
responds with an error message:
a := table("1st" = x, "2nd" = y): rectform(a)
Error: An arithmetical expression is expected. [rectform::new]
Use map
to
apply rectform
to the operands of such an object:
map(a, rectform)
This example illustrates the meaning of the three operands of
an object returned by rectform
.
We start with the expression x + sin(y),
for which rectform
is able to compute a complete
decomposition into real and imaginary part:
delete x, y: r := rectform(x + sin(y))
The first two operands of r
are the real
and imaginary part of the expression, and the third operand is 0:
op(r)
Next we consider the expression x + f(y),
where f(y) represents
an unknown function in a complex variable. rectform
can
split x into
its real and imaginary part, but fails to do this for the subexpression f(y):
delete f: r := rectform(x + f(y))
The first two operands of the returned object are the real and
the imaginary part of x,
and the third operand is the remainder f(y),
for which rectform
was not able to extract any
information about its real and imaginary part:
op(r)
Re(r), Im(r)
Sometimes rectform
is not able to extract
any information about the real and imaginary part of the input expression.
Then the third operand contains the whole input expression, possibly
in a rewritten form, due to the recursive mode of operation of rectform
.
The first two operands are 0.
Here is an example:
r := rectform(sin(x + f(y)))
op(r)
Re(r), Im(r)
Advanced users can extend rectform
to their
own special mathematical functions (see section "Backgrounds"
below). To this end, embed your mathematical function into a function environmentf
and
implement the behavior of rectform
for this function
as the "rectform"
slot of the function environment.
If a subexpression of the form f(u,..)
occurs
in z
, then rectform
issues the
call f::rectform(u,..)
to the slot routine to determine
the rectangular form of f(u,..)
.
For illustration, we show how this works for the sine function.
Of course, the function environment sin
already has a "rectform"
slot.
We call our function environment Sin
in order not
to overwrite the existing system function sin
:
Sin := funcenv(Sin): Sin::rectform := proc(u) // compute rectform(Sin(u)) local r, a, b; begin // recursively compute rectform of u r := rectform(u); if op(r, 3) <> 0 then // we cannot split Sin(u) new(rectform, 0, 0, Sin(u)) else a := op(r, 1); // real part of u b := op(r, 2); // imaginary part of u new(rectform, Sin(a)*cosh(b), cos(a)*sinh(b), 0) end_if end:
delete z: rectform(Sin(z))
If the if
condition is true, then rectform
is
unable to split u
completely into its real and
imaginary part. In this case, Sin::rectform
is
unable to split Sin(u)
into its real and imaginary
part and indicates this by storing the whole expression Sin(u)
in
the third operand of the resulting rectform
object:
delete f: rectform(Sin(f(z)))
op(%)

An arithmetical expression, a polynomial, a series expansion, an array, an hfarray, a list, or a set 
Element of the domain rectform
if z
is
an arithmetical
expression, and an object of the same type as z
otherwise.
Calling an element of rectform
as a function
yields the object itself, regardless of the arguments. The arguments
are not evaluated.
You can apply (almost) any function to elements of rectform
which
transforms a complexvalued expression into a complexvalued expression.
For example, you may add or multiply those elements, or apply
functions such as expand
and diff
to them. The result
of such an operation, which is not explicitely overloaded by a method
of rectform
(see below), is an element of rectform
.
This "automatic overloading" works as follows:
Each argument of the operation, which is an element of rectform
,
is converted to an expression using the method "expr"
(see
below). Then, the operation is applied and the result is reconverted
to an element of rectform
.
Use the function expr
to
convert an element of rectform
to an arithmetical
expression (as an element of a kernel domain).
The functions Re
and Im
return the real and imaginary part
of elements of rectform
.
An element z of rectform
consists
of three operands:
the real part of z,
the imaginary part of z,
the part of z, for that the real and imaginary part cannot be computed (possibly the integer 0, if there are not such subexpressions).
If a subexpression of the form f(u,..)
occurs
in z
and f
is a function environment, then rectform
attempts
to call the slot "rectform"
of f
to
determine the rectangular form of f(u,..)
. In this
way, you can extend the functionality of rectform
to
your own special mathematical functions.
The slot "rectform"
is called with the arguments u,..
of f
.
If the slot routine f::rectform
is not able to
determine the rectangular form of f(u,..)
, then
it should return new(rectform(0,0,f(u,..)))
. See Example 7. If f
does
not have a slot "rectform"
, then rectform
returns
the object new(rectform(0,0,f(u,..)))
for the corresponding
subexpression.
Similarly, if an element d
of a library domainT
occurs
as a subexpression of z
, then rectform
attempts
to call the slot "rectform"
of that domain with d
as
argument to compute the rectangular form of d
.
If the slot routine T::rectform
is not able
to determine the rectangular form of d
, then it
should return new(rectform(0,0,d))
.
If the domain T
does not have a slot "rectform"
,
then rectform
returns the object new(rectform(0,0,d))
for
the corresponding subexpression.