tesseract 4.1.1
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dppoint.cpp
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1/**********************************************************************
2 * File: dppoint.cpp
3 * Description: Simple generic dynamic programming class.
4 * Author: Ray Smith
5 * Created: Wed Mar 25 19:08:01 PDT 2009
6 *
7 * (C) Copyright 2009, Google Inc.
8 ** Licensed under the Apache License, Version 2.0 (the "License");
9 ** you may not use this file except in compliance with the License.
10 ** You may obtain a copy of the License at
11 ** http://www.apache.org/licenses/LICENSE-2.0
12 ** Unless required by applicable law or agreed to in writing, software
13 ** distributed under the License is distributed on an "AS IS" BASIS,
14 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 ** See the License for the specific language governing permissions and
16 ** limitations under the License.
17 *
18 **********************************************************************/
19
20#include "dppoint.h"
21#include "errcode.h"
22#include "tprintf.h"
23
24namespace tesseract {
25
26// Solve the dynamic programming problem for the given array of points, with
27// the given size and cost function.
28// Steps backwards are limited to being between min_step and max_step
29// inclusive.
30// The return value is the tail of the best path.
31DPPoint* DPPoint::Solve(int min_step, int max_step, bool debug,
32 CostFunc cost_func, int size, DPPoint* points) {
33 if (size <= 0 || max_step < min_step || min_step >= size)
34 return nullptr; // Degenerate, but not necessarily an error.
35 ASSERT_HOST(min_step > 0); // Infinite loop possible if this is not true.
36 if (debug)
37 tprintf("min = %d, max=%d\n",
38 min_step, max_step);
39 // Evaluate the total cost at each point.
40 for (int i = 0; i < size; ++i) {
41 for (int offset = min_step; offset <= max_step; ++offset) {
42 DPPoint* prev = offset <= i ? points + i - offset : nullptr;
43 int64_t new_cost = (points[i].*cost_func)(prev);
44 if (points[i].best_prev_ != nullptr && offset > min_step * 2 &&
45 new_cost > points[i].total_cost_)
46 break; // Find only the first minimum if going over twice the min.
47 }
48 points[i].total_cost_ += points[i].local_cost_;
49 if (debug) {
50 tprintf("At point %d, local cost=%d, total_cost=%d, steps=%d\n",
51 i, points[i].local_cost_, points[i].total_cost_,
52 points[i].total_steps_);
53 }
54 }
55 // Now find the end of the best path and return it.
56 int best_cost = points[size - 1].total_cost_;
57 int best_end = size - 1;
58 for (int end = best_end - 1; end >= size - min_step; --end) {
59 int cost = points[end].total_cost_;
60 if (cost < best_cost) {
61 best_cost = cost;
62 best_end = end;
63 }
64 }
65 return points + best_end;
66}
67
68// A CostFunc that takes the variance of step into account in the cost.
69int64_t DPPoint::CostWithVariance(const DPPoint* prev) {
70 if (prev == nullptr || prev == this) {
71 UpdateIfBetter(0, 1, nullptr, 0, 0, 0);
72 return 0;
73 }
74
75 int delta = this - prev;
76 int32_t n = prev->n_ + 1;
77 int32_t sig_x = prev->sig_x_ + delta;
78 int64_t sig_xsq = prev->sig_xsq_ + delta * delta;
79 int64_t cost = (sig_xsq - sig_x * sig_x / n) / n;
80 cost += prev->total_cost_;
81 UpdateIfBetter(cost, prev->total_steps_ + 1, prev, n, sig_x, sig_xsq);
82 return cost;
83}
84
85// Update the other members if the cost is lower.
86void DPPoint::UpdateIfBetter(int64_t cost, int32_t steps, const DPPoint* prev,
87 int32_t n, int32_t sig_x, int64_t sig_xsq) {
88 if (cost < total_cost_) {
89 total_cost_ = cost;
90 total_steps_ = steps;
91 best_prev_ = prev;
92 n_ = n;
93 sig_x_ = sig_x;
94 sig_xsq_ = sig_xsq;
95 }
96}
97
98} // namespace tesseract.
#define ASSERT_HOST(x)
Definition: errcode.h:88
DLLSYM void tprintf(const char *format,...)
Definition: tprintf.cpp:35
static DPPoint * Solve(int min_step, int max_step, bool debug, CostFunc cost_func, int size, DPPoint *points)
Definition: dppoint.cpp:31
int64_t CostWithVariance(const DPPoint *prev)
Definition: dppoint.cpp:69
int64_t(DPPoint::*)(const DPPoint *) CostFunc
Definition: dppoint.h:49