Hi Dan, I would suggest using one ezero with three different delr values for these three paths. You are introducting only one more variable. delr and ezero are correlated so by constraining delr you need more ezero values or vise versa. Shelly
-----Original Message----- From: dmc@pdx.edu [mailto:dmc@pdx.edu] Sent: Friday, October 29, 2004 10:25 AM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Fitting Commercial Molybdenum Disulfide
Mike & list,
Where can I find a reasonable model for my delr terms, if I do assume that the bond angles are changing/there is no isotropic expansion? Is there a description somewhere in the archives that I could look at?
Creating different sigma squared parameters for each path did help the R- Factor somewhat, but not the reduced chi. Here's some data:
Fit with seperate sigma's:
Independent points = 14.312500000 Number of variables = 6.000000000 Chi-square = 5778.957783654 Reduced Chi-square = 695.212966455 R-factor = 0.029041008 Measurement uncertainty (k) = 0.000181935 Measurement uncertainty (R) = 0.004860095 Number of data sets = 1.000000000
Guess parameters +/- uncertainties (initial guess): e0_1 = -4.0347670 +/- 2.9998980 (guessed as -4.072009 (1.919404)) ss = 0.0042860 +/- 0.0005990 (guessed as 0.004636 (0.000411)) e0 = 1.6770760 +/- 1.3230290 (guessed as 1.765958 (1.154388)) alpha = 0.0009180 +/- 0.0034050 (guessed as 0.001090 (0.002843)) ss2 = 0.0048160 +/- 0.0006910 (0.0000) ss3 = 0.0225310 +/- 0.0657250 (0.0000) Def parameters: delr_1 = 0.0036440 Set parameters: amp = 0.7
Correlations between variables: e0_1 and alpha --> 0.8542 e0 and alpha --> 0.8470 e0_1 and e0 --> 0.7407 e0_1 and ss3 --> 0.7060 alpha and ss3 --> 0.4715 ss2 and ss3 --> -0.4214 e0_1 and ss2 --> -0.3892 e0 and ss3 --> 0.3772 alpha and ss2 --> -0.2680 All other correlations are below 0.25
Fit without (original):
Independent points = 14.312500000 Number of variables = 4.000000000 Chi-square = 6562.747150128 Reduced Chi-square = 636.387602437 R-factor = 0.032979787 Measurement uncertainty (k) = 0.000181935 Measurement uncertainty (R) = 0.004860095 Number of data sets = 1.000000000
Guess parameters +/- uncertainties (initial guess): e0_1 = -4.0720130 +/- 1.9194050 (guessed as -4.072009 (1.919404)) ss = 0.0046360 +/- 0.0004110 (guessed as 0.004636 (0.000411)) e0 = 1.7659560 +/- 1.1543880 (guessed as 1.765958 (1.154388)) alpha = 0.0010900 +/- 0.0028430 (guessed as 0.001090 (0.002843))
Def parameters: delr_1 = 0.0043250
Set parameters: amp = 0.7
Correlations between variables: e0_1 and alpha --> 0.8416 e0 and alpha --> 0.8045 e0_1 and e0 --> 0.7141 All other correlations are below 0.25
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