Tag Archives: reference

Using Linux Shell Command within Python

If you just want to do some simple task, this would do:

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Half-Light Radii for Various Profiles

For a radial profile of , the enclosed flux within the radius is given by     I’m only concerned about azimuthal symmetric cases, so .  The idea is to solve     for . Gaussian Profile Say the Gaussian … Continue reading

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Comparing the Efficiencies of Gaussian Convolution Routines

These days I quite often need to convolve (i.e., smooth) 2D images by some Gaussian. There are quite a few routines that can do this with varying efficiencies. So I compared a couple of them. On my laptop, this script … Continue reading

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Some Physics Units Cheat Sheet

Before I forget: In CGS:     where        

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Estimating Standard Deviation from N Data Points

In astronomy people often estimate a standard deviation in, say, background counts from the observed data themselves, since it is very difficult to know what true standard deviations are. Then the question is this: How many measurements (e.g., the number … Continue reading

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Linux Image Manipulation Cheat Sheet

This will be my cheat sheet for doing image manipulation on Linux. Scale Images ImageMagick has a command mogrify to do this: This will scale all .jpg images to half the original size. Create a GIF Animation More to be … Continue reading

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Uncertainty in Flux and Magnitude

I keep forgetting this sort of simple algebra (aging is no fun), so here’s a note. Define magnitude to be related to flux as follows:     where is the zero point flux which defines the magnitude scale.  Let be … Continue reading

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Using Some Python 3 in Python 2.6.x

This is just a note for myself to start getting used to the Python 3 coding practices. In order to use some Python 3 features in Python 2.6.x, use this statement in my script: It’s not a very good idea … Continue reading

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