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# lect29 - • Correlation coefficient is dimensionless...

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UCF Physics: AST 5765/4762: (Advanced) Astronomical Data Analysis Fall 2009 Lecture Notes: 29. Cross Correlation 1 Check In: 10:30 — 10:35, 5 min Questions? 2 Cross Correlation: 10:35 – 11:20, 45 min Use cross-correlation to find shift: C ( s ) = integraldisplay -∞ f ( x + s ) g ( x ) dx (1) Evaluate for reasonable range of shifts, max is best alignment For spectrum shifts (e.g., Doppler), x = λ and s = Δ λ Discrete math, must generally: Generally, want to use f - ¯ f and g - ¯ g Generally need to pad data (see demo) Note: This is different from the correlation coefficient!
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Unformatted text preview: • Correlation coefficient is dimensionless, ranges [-1,1] ρ ( x, y ) = ∑ N i =1 ( x-μ x )( y-μ y ) Nσ x σ y (2) • It tests for trends (correlation) in sets of (x,y) datapoints • Cross correlation measures shifts between two datasets in the same independent variable • Assess the UNNORMALIZED correlation to do this • Demo: 19crosscor , start with Correlation_examples.png 3 Q&A: 11:20 – 11:45, 25 min 1...
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