Numerically integrating the Planck distribution

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Discussion Overview

The discussion revolves around the numerical integration of the Planck spectral distribution, specifically aiming to find the median wavelength where the radiance is equally distributed. The focus includes the effectiveness of different numerical integration methods at varying temperatures.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant reports using the composite Simpson rule for integration and achieving good convergence at temperatures around 5000K, but struggles with convergence at temperatures of 7000K and above.
  • Another participant questions the original poster's familiarity with numerical stability and the error term associated with Simpson's rule.
  • A third participant suggests that simpler methods, such as the trapezoidal rule with small intervals, may be more effective for numerical integration, especially when dealing with potentially problematic functions.
  • This participant acknowledges that while the trapezoidal rule may be inefficient, it is reliable and can be preferable unless integrating a large number of equations.
  • The same participant also mentions that composite Simpson's rule could be an improvement over the plain Simpson's rule for this specific problem.

Areas of Agreement / Disagreement

There is no consensus on the best numerical integration method for the Planck distribution, as participants express differing opinions on the effectiveness and reliability of various approaches.

Contextual Notes

Participants have not fully explored the implications of numerical stability or the specific error terms associated with the methods discussed, which may affect their conclusions.

heafnerj
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I'm working on a project that requires me to numerically integrate the Planck spectral distribution. The object is to find the median wavelength, with exactly 50% of the radiance on either side. I'm using a standard composite Simpson rule method and I get good convergence with temps around 5000K. For temps at and above 7000K, I can't get convergence. Is there a better scheme to use for this application?
 
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How familiar are you with issue of numeric stability? Have you analyzed the error term for Simpson's rule?
 
Hurkyl said:
How familiar are you with issue of numeric stability? Have you analyzed the error term for Simpson's rule?

Rudimentary. No.
 
Sometimes the simplest methods are the best when you are trying to solve numerical problems. When I am integrating something that I suspect might "misbehave" I always use methods based on polynomials of order 1; e.g. the trapezoidal rule with very small intervals.
This is very inefficient but it always works; and unless you need to integrate thousands of equations you will rarely notice the difference on a modern computer.

Of course you can always try to use e.g. the composite Simpson's rule; it should be better than the "plain" Simpson's rule for your problem.
 

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