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Commit ac3d216a authored by Amir MOHAMMADI's avatar Amir MOHAMMADI
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recompute far values in roc_for_far

parent 4bf48e9b
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1 merge request!48recompute far values in roc_for_far
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...@@ -421,73 +421,21 @@ bob::measure::roc_for_far(const blitz::Array<double, 1> &negatives, ...@@ -421,73 +421,21 @@ bob::measure::roc_for_far(const blitz::Array<double, 1> &negatives,
sort(negatives, neg, is_sorted); sort(negatives, neg, is_sorted);
sort(positives, pos, is_sorted); sort(positives, pos, is_sorted);
// do some magic to compute the FRR list
blitz::Array<double, 2> retval(2, n_points); blitz::Array<double, 2> retval(2, n_points);
// index into the FAR and FRR list // index into the FAR list
int far_index = n_points - 1; int far_index = n_points - 1;
int pos_index = 0, neg_index = 0;
int n_pos = pos.extent(0), n_neg = neg.extent(0);
// iterators into the result lists
auto pos_it = pos.begin(), neg_it = neg.begin();
// do some fast magic to compute the FRR values ;-)
do {
// check whether the current positive value is less than the current
// negative one
if (*pos_it < *neg_it) {
// increase the positive count
++pos_index;
// go to the next positive value
++pos_it;
} else {
// increase the negative count
++neg_index;
// go to the next negative value
++neg_it;
}
// check, if we have reached a new FAR limit,
// i.e. if the relative number of negative similarities is greater than
// 1-FAR (which is the CRR)
if (((double)neg_index / (double)n_neg > 1. - far_list(far_index)) &&
!(bob::core::isClose((double)neg_index / (double)n_neg,
1. - far_list(far_index), 1e-9, 1e-9))) {
// copy the far value
retval(0, far_index) = far_list(far_index);
// calculate the FRR for the current FAR
retval(1, far_index) = (double)pos_index / (double)n_pos;
// go to the next FAR value
--far_index;
}
// do this, as long as there are elements in both lists left and not all FRR // Get the threshold for the requested far values and calculate far and frr
// elements where calculated yet // values based on the threshold.
} while (pos_it != pos.end() && neg_it != neg.end() && far_index >= 0); while(far_index >= 0) {
// calculate the threshold for the requested far
// check if all FRR values have been set auto threshold = bob::measure::farThreshold(neg, pos, far_list(far_index), true);
if (far_index >= 0) { // calculate the frr and re-calculate the far
// walk to the end of both lists; at least one of both lists should already auto farfrr = bob::measure::farfrr(neg, pos, threshold);
// have reached its limit. retval(0, far_index) = farfrr.first;
while (pos_it != pos.end() && pos_it++ != pos.end()) retval(1, far_index) = farfrr.second;
++pos_index; far_index--;
while (neg_it != neg.end() && neg_it++ != neg.end())
++neg_index;
// fill in the remaining elements of the CAR list
do {
// copy the FAR value
retval(0, far_index) = far_list(far_index);
// check if the criterion is fulfilled (should be, as long as the lowest
// far is not below 0)
if ((double)neg_index / (double)n_neg > 1. - far_list(far_index)) {
// calculate the FRR for the current FAR
retval(1, far_index) = (double)pos_index / (double)n_pos;
} else {
// set FRR to 1 (this should never happen, but might be due to numerical
// issues)
retval(1, far_index) = 1.;
}
} while (far_index--);
} }
return retval; return retval;
......
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