Last modified: December 2018

URL: http://cxc.harvard.edu/sherpa/ahelp/polynomial.html
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AHELP for CIAO 4.11 Sherpa v1

polynomial

Context: models

Synopsis

Polynomial model of order 5.

Syntax

polynomial

Description

This model can be used with any one-dimensional data set since there are no units on the parameters.


Example

>>> create_model_component("polynomial", "mdl")
>>> print(mdl)

Create a component of the polynomial model and display its default parameters. The output is:

mdl
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.c0       thawed            1 -3.40282e+38  3.40282e+38           
   mdl.c1       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.c2       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.c3       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.c4       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.c5       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.offset   frozen            0 -3.40282e+38  3.40282e+38           

ATTRIBUTES

The attributes for this object are:

c0

The constant term.

c1

The amplitude of the (x-offset) term.

c2

The amplitude of the (x-offset)^2 term.

c3

The amplitude of the (x-offset)^3 term.

c4

The amplitude of the (x-offset)^4 term.

c5

The amplitude of the (x-offset)^5 term.

offset

There is a degeneracy between c0 and offset , so it is recommended that at least one of these remains frozen.

Notes

The functional form of the model for points is:

f(x) = sum_(i=0)^(i=8) c_i * (x - offset)^i

and for integrated data sets the low-edge of the grid is used.


Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

models
powerlaw