Last modified: December 2020

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AHELP for CIAO 4.13 Sherpa v1


Context: models


One-dimensional polynomial function of order 8.




The maximum order of the polynomial is 8. The default setting has all parameters frozen except for c0 , which means that the model acts as a constant.


>>> create_model_component("polynom1d", "mdl")
>>> print(mdl)

Create a component of the polynom1d model and display its default parameters. The output is:

   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.c6       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.c7       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.c8       frozen            0 -3.40282e+38  3.40282e+38           
   mdl.offset   frozen            0 -3.40282e+38  3.40282e+38           


The attributes for this object are:

Attribute Definition
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.
c6 The amplitude of the (x-offset)^6 term.
c7 The amplitude of the (x-offset)^7 term.
c8 The amplitude of the (x-offset)^8 term.
offset There is a degeneracy between c0 and offset , so it is recommended that at least one of these remains frozen.


The functional form of the model for points is:

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

and for an integrated grid it is the integral of this over the bin.


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

See Also

polynom2d, powlaw1d