Create a PolyMap
A PolyMap is a form of Mapping which performs a general polynomial transformation. Each output coordinate is a polynomial function of all the input coordinates. The coefficients are specified separately for each output coordinate. The forward and inverse transformations are defined independantly by separate sets of coefficients. If no inverse transformation is supplied, the default behaviour is to use an iterative method to evaluate the inverse based only on the forward transformation (see attribute IterInverse).
"
ncoeff_f$\ast $( 2
$+$ nin )"
elements.
Each group of "
2 $+$
nin"
adjacent elements describe a single coefficient of the forward transformation.
Within each such group, the first element is the coefficient value; the next element is
the integer index of the PolyMap output which uses the coefficient within its
defining polynomial (the first output has index 1); the remaining elements of the
group give the integer powers to use with each input coordinate value (powers
must not be negative, and floating point values are rounded to the nearest
integer). If "
ncoeff_f"
is zero, a NULL pointer may be supplied for "
coeff_f"
.
For instance, if the PolyMap has 3 inputs and 2 outputs, each group consisting of 5
elements, A groups such as "
(1.2, 2.0, 1.0, 3.0, 0.0)"
describes a coefficient with
value 1.2 which is used within the definition of output 2. The output value is
incremented by the product of the coefficient value, the value of input coordinate 1
raised to the power 1, and the value of input coordinate 2 raised to the power 3. Input
coordinate 3 is not used since its power is specified as zero. As another example, the
group "
(-1.0, 1.0, 0.0, 0.0, 0.0 )"
describes adds a constant value -1.0 onto output
1 (it is a constant value since the power for every input axis is given as
zero).
Each final output coordinate value is the sum of the "
ncoeff_f"
terms described by the "
ncoeff_f"
groups within the supplied array.
"
ncoeff_i$\ast $( 2
$+$ nout )"
elements.
Each group of "
2 $+$
nout"
adjacent elements describe a single coefficient of the inverse transformation,
using the same schame as "
coeff_f"
, except that "
inputs"
and "
outputs"
are transposed. If "
ncoeff_i"
is zero, a NULL pointer may be supplied for
"
coeff_i"
. "
printf"
format specifiers identified by "
%"
symbols in the
normal way. "
options"
string contains "
%"
format specifiers,
then an optional list of additional arguments may follow it in order to supply
values to be substituted for these specifiers. The rules for supplying these are
identical to those for the astSet function (and for the C "
printf"
function). A null Object pointer (AST__NULL) will be returned if this function is invoked with the AST error status set, or if it should fail for any reason.