1 /*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "core/statistics.h"
18
19 #include <math.h>
20
21 namespace android {
22 namespace filterfw {
23
IncrementalGaussian()24 IncrementalGaussian::IncrementalGaussian()
25 : n_(0),
26 sum_x_(0.0f),
27 sum_x2_(0.0f),
28 mean_(0.0f),
29 var_(0.0f),
30 exp_denom_(0.0f),
31 pdf_denom_(0.0f) {
32 }
33
Add(float value)34 void IncrementalGaussian::Add(float value) {
35 ++n_;
36 sum_x_ += value;
37 sum_x2_ += value * value;
38
39 mean_ = sum_x_ / n_;
40 var_ = sum_x2_ / n_ - mean_ * mean_;
41
42 exp_denom_ = 2.0f * var_;
43 pdf_denom_ = sqrtf(M_PI * exp_denom_);
44 }
45
Std() const46 float IncrementalGaussian::Std() const {
47 return sqrtf(var_);
48 }
49
Pdf(float value) const50 float IncrementalGaussian::Pdf(float value) const {
51 if (var_ == 0.0f) { return n_ > 0 ? value == mean_ : 0.0f; }
52 const float diff = value - mean_;
53 return expf(-diff * diff / exp_denom_) / pdf_denom_;
54 }
55
56 } // namespace filterfw
57 } // namespace android
58