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RCURVECOMMONNONLINEAR procedure

Refits a standard curve with common nonlinear parameters across groups to provide s.e.’s for linear parameters (R.W. Payne).

Options

PRINT = string tokens Printed output from the analysis (model, deviance, summary, estimates, correlations, fittedvalues, accumulated, monitoring); default mode, summ, esti
MAXCYCLE = variate Maximum number of iterations; default 30
METHOD = string token Algorithm for fitting nonlinear model (gaussnewton, newtonraphson, fletcherpowell); default newt
STEPLENGTHS = scalar or variate Initial step lengths for the parameters
SAVE = regression save structure Save structure from this analysis
INSAVE = regression save structure Save structure for the curve fitted by FITCURVE, default takes the most recent regression analysis

No parameters

Description

RCURVECOMMONNONLINEAR can be used after a FITCURVE analysis to refit a standard curve that has common nonlinear parameters across groups. It uses the CALCULATION option of FIT, which provides standard errors for the linear parameters. These are unavailable with FITCURVE.

The INSAVE option can provide the regression save structure from the FITCURVE analysis. If this is not set, the save structure from the most recent regression analysis is used. A fault is given if the save structure is not from a FITCURVE analysis with groups and common nonlinear parameters. The SAVE option saves the regression save structure from this analysis.

The PRINT option controls printed output, with the same settings as FITCURVE. The other options control aspects of the optimization. MAXCYCLE specifies the maximum number of iterations to be used to estimate the nonlinear parameters; default 30. METHOD specifies the algorithm to be used. The default is Newton Raphson, which is the same method as FITCURVE. STEPLENGTHS defines step lengths for the estimation of the nonlinear parameters. FITCURVE uses a different strategy from FIT. It includes nonlinear parameters for all the groups in the model, but constrains them to be equal when they are common across groups. Consequently RCURVECOMMONNONLINEAR may obtain slightly different parameter estimates from the original FITCURVE analysis. Modifying these options may enable you to obtain closer results.

Options: PRINT, MAXCYCLE, METHOD, STEPLENGTHS, SAVE, INSAVE.
Parameters: none.

Action with RESTRICT

Any restriction applied to vectors used in the regression model applies also to the results from RCURVECOMMONNONLINEAR.

See also

Directives: FIT, FITCURVE.
Commands for: Regression analysis.

Example

CAPTION    'RCURVECOMMONNONLINEAR example',\
           !t('Relationship between yield of sugar from sugar beet',\
           'and phosphorus in different years'); STYLE=meta,plain
VARIATE    [NVALUES=64] Beetwt,%sugar,SoilP,Sugar
READ       Beetwt,%sugar,SoilP
           7.23 18.5  5.4   7.69 18.0  5.4  24.64 20.1  7.8  26.67 19.8  8.0
           39.78 19.5 18.0  44.98 19.3 15.6  41.59 19.7 30.4  44.08 19.8 33.8
           48.37 19.4 50.4  44.76 19.0 51.0  49.73 18.6 44.0  51.54 18.5 40.2
           47.69 19.0 57.2  45.66 19.4 65.0  50.18 18.6 27.0  47.69 18.7 30.0

            8.82 13.8  5.6   1.81 13.9  4.8  15.82 14.5 10.2   9.04 14.0  8.6
           24.41 15.0 21.6  22.60 14.1 17.2  26.45 15.2 36.4  20.80 15.3 37.2
           28.30 14.2 44.4  22.60 14.7 44.4  14.24 13.5 41.0  35.94 15.6 30.2
           25.54 15.8 60.8  27.13 15.6 47.0  31.42 15.6 27.0  34.13 15.4 29.0

           19.90 16.1  3.0  20.60 16.0  2.0  34.70 16.7  6.2  35.40 16.4  6.2
           46.80 17.1 19.8  40.50 16.9 17.2  43.00 16.9 29.6  48.60 17.1 28.0
           47.30 17.0 42.8  41.30 17.1 46.2  44.30 17.0 36.6  47.60 16.6 40.0
           45.60 17.0 42.2  44.60 17.0 52.0  44.00 17.2 23.4  40.10 16.6 28.0

           14.35 16.1  4.0  14.35 15.5  3.8  26.71 16.6  8.0  25.12 16.4  6.4
           33.39 17.2 18.2  33.79 16.2 14.8  36.68 17.0 35.0  33.69 16.8 29.6
           34.98 17.0 37.2  35.78 17.0 40.0  42.06 17.2 39.6  38.77 17.3 36.8
           40.66 17.3 52.4  37.28 17.2 45.6  34.68 17.3 22.0  32.59 17.2 26.0
           : 
CALCULATE  Sugar = Beetwt * %sugar / 100  
FACTOR     [LEVELS=4; VALUES=16(1...4)] Year
MODEL      Sugar
TERMS      SoilP*Year
FITCURVE   [PRINT=model,estimates; CURVE=lexp] SoilP
ADD        Year
&          SoilP.Year
&          [PRINT=accumulated; NONLINEAR=separate; FPROBABILITY=yes]
DROP       [PRINT=*; NONLINEAR=common]
RCURVECOMMONNONLINEAR
Updated on February 1, 2022

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