add AND algorithm

bob/fusion/base/algorithm/AND.py

+#!/usr/bin/env python
+
+from __future__ import division
+from __future__ import absolute_import
+
+import numpy
+
+from .Algorithm import Algorithm
+
+import bob.core
+logger = bob.core.log.setup("bob.fusion.base")
+
+
+class AND(Algorithm):
+    """This algorithm fuses several systems with cascading."""
+
+    def __init__(self, thresholds=None, *args, **kwargs):
+        super(AND, self).__init__(
+            classifier=self,
+            thresholds=thresholds,
+            *args, **kwargs)
+        self.thresholds = thresholds
+
+    def fit(self, X, y):
+        pass
+
+    def decision_function(self, scores):
+        if self.thresholds is None:
+            ValueError('No threshold was specified.')
+
+        for i, th in enumerate(self.thresholds):
+            mask = scores[:, i + 1] < th
+            scores[mask, i + 1] = numpy.nan
+
+        mask = numpy.sum(numpy.isnan(scores[:, 1:]), axis=1, dtype=bool)
+        new_scores = numpy.array(scores[0])
+        new_scores[mask] = numpy.finfo('float16').min
+        return new_scores