Description of slgetroc

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slgetroc

PURPOSE

SLGETROC Computes some point from ROC Curve

SYNOPSIS

function [thr, fa, fr] = slgetroc(thrs, fars, frrs, item, itempara)

DESCRIPTION

SLGETROC Computes some point from ROC Curve

 $ Syntax $
   - [thr, fa, fr] = slgetroc(thrs, fars, frrs, item, itempara)

 $ Arguments $
   - thrs:         the sampled threshold values
   - fars:         the false accept rates at the sampled thresholds
   - frrs:         the false reject rates at the sampled thresholds
   - item:         the items to be evaluated
   - itempara:     the extra parameter for the item
   - thr:          the threshold at which the specified point is reached
   - fa:           the false accept rate at the selected point
   - fr:           the false reject rate at the selected point
   
 $ Description $
   [thr, fa, fr] = slgetroc(thrs, fars, frrs, item, itempara) Computes 
   a required point from the ROC curves specified by thrs, fars, and 
   frrs. The requirement on the point is specified by item and itempara.
   \*
   \t   Table 1.  The Items of ROC Retrieval    \\
   \h      name     &    description            \\
          'ratio'   &  solves the point where fr / fa = itempara   \\
          'fixfa'   &  solves the point where fa = itempara        \\
          'fixfr'   &  solves the point where fr = itempara        \\
          'fixth'   &  solves the point where threshold = itempara \\
          'best'    &  finds the point where 
                       itempara * fa + (1 - itempara) * fr attains min. \\
   \*

 $ Remarks $
   - To increase accuracy, inverse-interpolation technique is used.

 $ History $
   - Created by Dahua Lin on Jun 10th, 2005
   - Modified by Dahua Lin on May 1st, 2006
     - Base on the sltoolbox v4

CROSS-REFERENCE INFORMATION

This function calls:

• raise_lackinput RAISE_LACKINPUT Raises an error indicating lack of input argument
• slignorevars SLIGNOREVARS Ignores the input variables

This function is called by:

SUBFUNCTIONS

• function f = make_mono(f)

SOURCE CODE

0001 function [thr, fa, fr] = slgetroc(thrs, fars, frrs, item, itempara)
0002 %SLGETROC Computes some point from ROC Curve
0003 %
0004 % $ Syntax $
0005 %   - [thr, fa, fr] = slgetroc(thrs, fars, frrs, item, itempara)
0006 %
0007 % $ Arguments $
0008 %   - thrs:         the sampled threshold values
0009 %   - fars:         the false accept rates at the sampled thresholds
0010 %   - frrs:         the false reject rates at the sampled thresholds
0011 %   - item:         the items to be evaluated
0012 %   - itempara:     the extra parameter for the item
0013 %   - thr:          the threshold at which the specified point is reached
0014 %   - fa:           the false accept rate at the selected point
0015 %   - fr:           the false reject rate at the selected point
0016 %
0017 % $ Description $
0018 %   [thr, fa, fr] = slgetroc(thrs, fars, frrs, item, itempara) Computes
0019 %   a required point from the ROC curves specified by thrs, fars, and
0020 %   frrs. The requirement on the point is specified by item and itempara.
0021 %   \*
0022 %   \t   Table 1.  The Items of ROC Retrieval    \\
0023 %   \h      name     &    description            \\
0024 %          'ratio'   &  solves the point where fr / fa = itempara   \\
0025 %          'fixfa'   &  solves the point where fa = itempara        \\
0026 %          'fixfr'   &  solves the point where fr = itempara        \\
0027 %          'fixth'   &  solves the point where threshold = itempara \\
0028 %          'best'    &  finds the point where
0029 %                       itempara * fa + (1 - itempara) * fr attains min. \\
0030 %   \*
0031 %
0032 % $ Remarks $
0033 %   - To increase accuracy, inverse-interpolation technique is used.
0034 %
0035 % $ History $
0036 %   - Created by Dahua Lin on Jun 10th, 2005
0037 %   - Modified by Dahua Lin on May 1st, 2006
0038 %     - Base on the sltoolbox v4
0039 %
0040 
0041 %% Parse and Verify
0042 if nargin < 4
0043     raise_lackinput('slgetroc', 5);
0044 end
0045 if ~isequal(size(thrs), size(fars)) || ~isequal(size(thrs), size(frrs))
0046     error('sltoolbox:sizmismatch', ...
0047         'The sizes of thrs, fars and frrs are not consistent');
0048 end
0049 thrs = thrs(:);
0050 fars = fars(:);
0051 frrs = frrs(:);
0052 
0053 % preprocessing (make it strictly monotonical)
0054 fars = make_mono(fars);
0055 frrs = make_mono(frrs);
0056 
0057 %% Compute
0058 usemethod = 'linear';
0059 switch item
0060     case 'ratio'
0061         ratios = frrs ./ max(fars, eps);
0062         if nargin < 5 || isempty(itempara)
0063             itempara = 1;
0064         end
0065         thr = interp1(ratios, thrs, itempara, usemethod);
0066     case 'fixfa'
0067         if nargin < 5 || isempty(itempara)
0068             itempara = 0.1;
0069         end
0070         thr = interp1(fars, thrs, itempara, usemethod);
0071     case 'fixfr'
0072         if nargin < 5 || isempty(itempara)
0073             itempara = 0.1;
0074         end
0075         thr = interp1(frrs, thrs, itempara, usemethod);
0076     case 'fixth'
0077         if nargin < 5 || isempty(itempara)
0078             error('You must specify the parameter for fixth item');
0079         end 
0080         thr = itempara;
0081     case 'best'
0082         if nargin < 5 || isempty(itempara)
0083             itempara = 0.5;
0084         end
0085         [mv, p] = min(itempara * fars + (1 - itempara) * frrs);
0086         slignorevars(mv);
0087         thr = thrs(p);
0088     otherwise
0089         error('sltoolbox:invalidarg', ...
0090             'Invalid item %s for slgetroc', item);
0091 end
0092 
0093 fa = interp1(thrs, fars, thr, usemethod);
0094 fr = interp1(thrs, frrs, thr, usemethod);
0095 
0096 
0097 function f = make_mono(f)
0098 
0099 df = diff(f);
0100 
0101 if f(end) >= f(1)
0102     df = max(df, eps);
0103 else
0104     df = min(df, -eps);
0105 end
0106 f = [f(1); f(1) + cumsum(df)];
0107 
0108 
0109 
0110 
0111

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