Last modified: December 2023

AHELP for CIAO 4.16 Sherpa


Context: models


One-dimensional box function.




The model is flat between xlow and xhi (both limits are inclusive), where it is set to the ampl parameter. Outside this range the model is zero.


>>> create_model_component("box1d", "mdl")
>>> print(mdl)

Create a component of the box1d model and display its default parameters. The output is:

   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.xlow     thawed            0 -3.40282e+38  3.40282e+38           
   mdl.xhi      thawed            1 -3.40282e+38  3.40282e+38           
   mdl.ampl     thawed            1 -3.40282e+38  3.40282e+38           


The attributes for this object are:

Attribute Definition
xlow Coordinate of the lower cut-off.
xhi Coordinate of the upper cut-off.
ampl The amplitude of the box.


The functional form of the model for points is:

f(x) = ampl if xlow <= x <= xhi
     = 0       otherwise

and for an integrated grid it is:

f(lo,hi) = ampl         if lo >= xlow and hi <= xhi
         = 0            if hi <= xlow or lo >= xhi
         = ampl * g     where g is the fraction of lo,hi
                        that falls within xlo,xhi

This behavior is different to how the amplitude is handled in other models, such as const1d .

Changes in CIAO

Changed in CIAO 4.16

The default value for the xhi parameter has been changed from 0 to 1, and the range of ampl now matches xlow and xhi rather than being set to -1 to 1.


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

See Also

box2d, const1d, delta1d, scale1d, stephi1d, steplo1d