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A Library for Handling
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Description:
This
function evaluates the rate of change of a specified output of the supplied
Mapping
with respect to a specified input, at a specified input position.
The result is estimated by interpolating the function using a fourth order polynomial
in the neighbourhood of the specified position. The size of the neighbourhood used is
chosen to minimise the RMS residual per unit length between the interpolating polynomial
and the supplied Mapping function. This method produces good accuracy but can involve
evaluating the Mapping 100 or more times.
Synopsis
double astRate( AstMapping
this,
double at,
int ax1, int ax2 )
Parameters:
this
Pointer to the Mapping to be applied.
at
The address of an array holding the axis values at the position at which the rate of
change is to be evaluated. The number of elements in this array should equal the number
of inputs to the Mapping.
ax1
The index of the Mapping output for which the rate
of change is to be found (output numbering starts at 1 for the first output).
ax2
The index of the Mapping input which is to be varied in order to find the rate of
change (input numbering starts at 1 for the first input).
Returned Value
astRate()
The rate of change of Mapping output "
ax1"
with respect to input "
ax2"
,
evaluated at "
at"
, or AST__BAD if the value cannot be calculated.
Notes:
Copyright (C) 2021 East Asian Observatory
- ←Prev
- AST
A Library for Handling
World
Coordinate Systems
in Astronomy - Next→
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