Frpcr
Purpose
Full-ratio PCR calibration and prediction.
Synopsis
- model = frpcr(x,y,ncomp,options) %calibration
- pred = frpcr(x,model,options) %prediction
- valid = frpcr(x,y,model,options) %validation
Description
FRPCR calculates a single full-ratio PCR model using the given number of components ncomp to predict y from measurements x. Random multiplicative scaling of each sample can be used to aid model stability. Full-Ratio PCR models are based on the simultaneous regression for both y-block prediction and scaling variations (such as those due to pathlength and collection efficiency variations). The resulting PCR model is insensitive to absolute scaling errors.
NOTE: For best results, the x-block should not be mean-centered.
Inputs are x the predictor block (2-way array or dataset object), y the predicted block (2-way array or dataset object), ncomp the number of components to to be calculated (positive integer scalar) and the optional options structure, options.
The output of the function is a standard model structure model. In prediction and validation modes, the same model structure is used but predictions are provided in the model.detail.pred field.
Although the full-ratio method uses a different method for determination of the regression vector, the fundamental idea is very similar to the optimized scaling 2 method as described in:
T.V. Karstang and R. Manne, "Optimized scaling: A novel approach to linear calibration with close data sets", Chemom. Intell. Lab. Syst., 14, 165-173 (1992).
Inputs
- x = input x-block (should not be mean-centered), 2-way double array or dataset object.
- y = input y-block, 2-way double array or dataset object, calibration and validation modes.
- ncomp = number of components, calibration mode.
- model = existing model, prediction and validation modes.
Outputs
- model = model generated in calibration mode.
- pred = prediction results, prediction mode.
- valid = validation results, validation mode.
Options
options = a structure with the following fields:
- pathvar: [ {0.2} ] standard deviation for random multiplicative scaling. A value of zero will disable the random sample scaling but may increase model sensitivity to scaling errors,
- useoffset: [ {'off'} | 'on' ] flag determining use of offset term in regression equations (may be necessary for mean-centered x-block),
- display: [ {'off'} | 'on' ] governs level of display to command window,
- plots: [ {'none'} | 'intermediate' | 'final' ] governs level of plotting,
- preprocessing: {[ ] [ ]} cell of two preprocessing structures (see PREPROCESS) defining preprocessing for the x- and y-blocks.
- algorithm: [ {'direct'} | 'empirical' ] governs solution algorithm. Direct solution is fastest and most stable. Only empirical will work on single-factor models when useoffset is 'on', and
- blockdetails: [ 'compact' | {'standard'} | 'all' ] level of detail (predictions, raw residuals, and calibration data) included in the model.
- ‘Standard’ - the predictions and raw residuals for the X-block as well as the X-block itself are not stored in the model to reduce its size in memory. Specifically, these fields in the model object are left empty: 'model.pred{1}', 'model.detail.res{1}', 'model.detail.data{1}'.
- ‘Compact’ = for this function, 'compact' is identical to 'standard'.
- 'All' = keep predictions, raw residuals for both X- & Y-blocks as well as the X- & Y-blocks themselves.
- confidencelimit: [ {'0.95'} ] Confidence level for Q and T2 limits. A value of zero (0) disables calculation of confidence limits.
In addition, there are several options relating to the algorithm. See FRPCRENGINE.