Summary
libdedx currently interpolates stopping-power tables with natural cubic splines in linear space.
For ICRU data, the recommended interpolation is instead log-log interpolation with natural cubic splines, i.e. fitting ln(X) as a function of ln(T), where X is the stopping power and T is the energy.
From ICRU:
The main results are given to four significant figures, more than are warranted by the expected accuracy of the evaluations, in order to facilitate smooth interpolation. Based on practices used in the development of these tables, log-log interpolation is recommended, using natural cubic splines fitted to ln X as a function of ln T, where X is the variable of interest.
Requested behavior
- Use log-log natural cubic spline interpolation for tabulated stopping-power data by default.
- Keep linear interpolation available as an explicit runtime option.
- Return the exact tabulated value when queried exactly at a knot energy.
Why this matters
The interpolation method affects off-grid values and can give noticeable differences compared with the intended source-table behavior. Also, knot points should reproduce the tabulated data exactly.
Summary
libdedxcurrently interpolates stopping-power tables with natural cubic splines in linear space.For ICRU data, the recommended interpolation is instead log-log interpolation with natural cubic splines, i.e. fitting
ln(X)as a function ofln(T), whereXis the stopping power andTis the energy.From ICRU:
Requested behavior
Why this matters
The interpolation method affects off-grid values and can give noticeable differences compared with the intended source-table behavior. Also, knot points should reproduce the tabulated data exactly.