Im
Imaginary part of an arithmetical expression
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Im(z
) Im(L
)
Im(z)
returns the imaginary part of z
.
The intended use of Im
is for constant arithmetical expressions.
Especially for numbers,
of type DOM_INT
, DOM_RAT
, DOM_FLOAT
,
or DOM_COMPLEX
,
the imaginary part is computed directly and very efficiently.
Im
can handle symbolic expressions. Properties
of identifiers are taken into account. See assume
. An identifier without any property
is assumed to be complex. See Example 2.
If Im
cannot extract the whole imaginary
part of z
, then the returned expression contains
symbolic Re
and Im
calls. In
such cases, try using the rectform
function.
See Example 3. Note that using rectform
is
computationally expensive.
The Im
function is automatically mapped to
all entries of container objects such as arrays, lists, matrices,
polynomials, sets, and tables.
This function is sensitive to properties of identifiers set
via assume
.
The imaginary part of 2 e^{1 + i} is:
Im(2*exp(1 + I))
Im
cannot extract the imaginary part of symbolic
expressions containing identifiers without a value. However, in some
cases it can still simplify the input expression, as in the following
two examples:
Im(u + v*I)
Im(z + 2)
By default, identifiers without a value are assumed to represent
arbitrary complex numbers. You can use assume
to change this. The following
command tells the system that z
represents only
imaginary numbers:
assume(z, Type::Imaginary): Im(z + 2*I)
unassume(z)
If Im
cannot extract the imaginary part of
a symbolic expression, try using the function rectform
. It splits a complex expression z into
its real and imaginary part and is more powerful than Im
:
Im(exp(I*sin(z))); r := rectform(exp(I*sin(z)))
Then use Im(r)
to extract the imaginary part
of r
:
Im(r)
Symbolic expressions of type "Im"
always
have the property Type::Real
, even if
no identifier of the symbolic expression has a property:
is(Im(sin(2*x)), Type::Real)
You can extend the functions Re
and Im
to
their own special mathematical functions. See the “Algorithms”
section. To do so, embed your mathematical function into a function environmentf
and
implement the behavior of the functions Re
and Im
for
this function as the slots "Re"
and "Im"
of
the function environment.
If a subexpression of the form f(u,..)
occurs
in z
, then Re
and Im
issue
the call f::Re(u,..)
and f::Im(u,..)
,
respectively, to the slot routine to determine the real and the imaginary
part of f(u,..)
, respectively.
For example, extend the function Im
for the
sine function. Of course, the function environment sin
already has a "Im"
slot.
Call your function environment Sin
in order not
to overwrite the existing system function sin
:
Sin := funcenv(Sin): Sin::Im := proc(u) // compute Im(Sin(u)) local r, s; begin r := Re(u); if r = u then return(0) elif not has(r, {hold(Im), hold(Re)}) then s := Im(u); if not has(s, {hold(Im), hold(Re)}) then return(cos(r)*sinh(s)) end_if end_if; return(FAIL) end:
Im(Sin(2)), Im(Sin(3*I)), Im(Sin(2 + 3*I))
The return value FAIL
tells the function Im
that Sin::Im
was
unable to determine the imaginary part of the input expression. The
result is then a symbolic Im
call:
Im(2 + Sin(f(z)))
 

A container object: an array, an hfarray, a list, a matrix, a polynomial, a set, or a table. 
arithmetical expression or a container object containing such expressions
z
If a subexpression of the form f(u,...)
occurs
in z
and f
is a function environment, then Im
attempts
to call the slot "Im"
of f
to
determine the imaginary part of f(u,...)
. In this
way, you can extend the functionality of Im
to
your own special mathematical functions.
The slot "Im"
is called with the arguments u
,...
of f
. If the slot routine f::Im
is
not able to determine the imaginary part of f(u,...)
,
then it must return FAIL
.
If f
does not have a slot "Im"
,
or if the slot routine f::Im
returns FAIL
,
then f(u,...)
is replaced by the symbolic call Im(f(u,...))
in
the returned expression. See Example 5.
Similarly, if an element d
of a library domainT
occurs
as a subexpression of z
, then Im
attempts
to call the slot "Im"
of that domain with d
as
argument to compute the imaginary part of d
.
If the slot routine T::Im
is not able to
determine the imaginary part of d
, then it must
return FAIL
.
If T
does not have a slot "Im"
,
or if the slot routine T::Im
returns FAIL
,
then d
is replaced by the symbolic call Im(d)
in
the returned expression.