[plot] add basic plotter support

include/CMakeLists.txt

@@ -46,6 +46,7 @@ target_sources(
             "HEADERS"
             FILES
             "fcarouge/kalman.hpp"
+            "fcarouge/printer.hpp"
             "fcarouge/utility.hpp")
 install(
   TARGETS kalman

include/fcarouge/internal/format.hpp

@@ -46,6 +46,9 @@ For more information, please refer to <https://unlicense.org> */
 
 namespace fcarouge {
 template <typename> class kalman;
+namespace decorator {
+template <typename> class printer;
+}
 } // namespace fcarouge
 
 template <typename Filter, typename Char>
@@ -61,8 +64,9 @@ struct std::formatter<fcarouge::kalman<Filter>, Char> {
 
   //! @todo P2585 may be useful in simplifying and standardizing the support.
   template <typename OutputIt>
-  auto format(const fcarouge::kalman<Filter> &filter,
-              std::basic_format_context<OutputIt, Char> &format_context) const
+  constexpr auto
+  format(const fcarouge::kalman<Filter> &filter,
+         std::basic_format_context<OutputIt, Char> &format_context) const
       -> OutputIt {
 
     format_context.advance_to(
@@ -141,4 +145,8 @@ struct std::formatter<fcarouge::kalman<Filter>, Char> {
   }
 };
 
+template <typename Filter, typename Char>
+struct std::formatter<fcarouge::decorator::printer<Filter>, Char>
+    : public std::formatter<Filter, Char> {};
+
 #endif // FCAROUGE_INTERNAL_FORMAT_HPP

include/fcarouge/kalman.hpp

@@ -48,6 +48,7 @@ For more information, please refer to <https://unlicense.org> */
 
 #include "internal/factory.hpp"
 #include "internal/format.hpp"
+#include "printer.hpp"
 #include "utility.hpp"
 
 #include <concepts>
@@ -131,7 +132,7 @@ namespace fcarouge {
 //! https://arxiv.org/pdf/1905.13002.pdf ? GPU implementation? Parallel
 //! implementation?
 template <typename Filter>
-class kalman final : public internal::conditional_member_types<Filter> {
+class kalman : public internal::conditional_member_types<Filter> {
 private:
   //! @name Private Member Types
   //! @{

include/fcarouge/printer.hpp

@@ -0,0 +1,95 @@
+/*  __          _      __  __          _   _
+| |/ /    /\   | |    |  \/  |   /\   | \ | |
+| ' /    /  \  | |    | \  / |  /  \  |  \| |
+|  <    / /\ \ | |    | |\/| | / /\ \ | . ` |
+| . \  / ____ \| |____| |  | |/ ____ \| |\  |
+|_|\_\/_/    \_\______|_|  |_/_/    \_\_| \_|
+
+Kalman Filter
+Version 0.4.0
+https://github.com/FrancoisCarouge/Kalman
+
+SPDX-License-Identifier: Unlicense
+
+This is free and unencumbered software released into the public domain.
+
+Anyone is free to copy, modify, publish, use, compile, sell, or
+distribute this software, either in source code form or as a compiled
+binary, for any purpose, commercial or non-commercial, and by any
+means.
+
+In jurisdictions that recognize copyright laws, the author or authors
+of this software dedicate any and all copyright interest in the
+software to the public domain. We make this dedication for the benefit
+of the public at large and to the detriment of our heirs and
+successors. We intend this dedication to be an overt act of
+relinquishment in perpetuity of all present and future rights to this
+software under copyright law.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
+
+For more information, please refer to <https://unlicense.org> */
+
+#ifndef FCAROUGE_PRINTER_HPP
+#define FCAROUGE_PRINTER_HPP
+
+#include <print>
+
+namespace fcarouge {
+namespace decorator {
+template <typename Filter> class printer : public Filter {
+public:
+  using Filter::p;
+  using Filter::x;
+
+  inline constexpr explicit printer([[maybe_unused]] Filter &&filter)
+      : Filter{std::forward<Filter>(filter)} {
+    std::println("{{\"event\": \"construction\", \"filter\":{}}}", *this);
+  }
+
+  inline constexpr ~printer() {
+    std::println("{{\"event\": \"destruction\", \"filter\":{}}}", *this);
+  }
+
+  inline constexpr void x(const auto &value, const auto &...values) {
+    Filter::x(value, values...);
+    std::println("{{\"event\": \"x\", \"filter\":{}}}", *this);
+  }
+
+  //! @todo Implement the remaining events.
+  inline constexpr void p(const auto &value, const auto &...values) {
+    Filter::p(value, values...);
+    std::println("{{\"event\": \"p\", \"filter\":{}}}", *this);
+  }
+
+  inline constexpr void predict(const auto &...arguments) {
+    Filter::predict(arguments...);
+    std::println("{{\"event\": \"predict\", \"filter\":{}}}", *this);
+  }
+
+  inline constexpr void update(const auto &...arguments) {
+    Filter::update(arguments...);
+    std::println("{{\"event\": \"update\", \"filter\":{}}}", *this);
+  }
+};
+} // namespace decorator
+
+struct printer_decorator {};
+
+inline constexpr printer_decorator printer;
+
+template <typename Filter>
+inline constexpr auto
+operator|(Filter &&filter, [[maybe_unused]] const printer_decorator decorator) {
+  return decorator::printer<Filter>(std::forward<Filter>(filter));
+}
+
+} // namespace fcarouge
+
+#endif // FCAROUGE_PRINTER_HPP

sample/kf_1x1x0_building_height.cpp

@@ -3,6 +3,8 @@
 #include <cassert>
 #include <cmath>
 
+#include <iostream>
+
 namespace fcarouge::sample {
 namespace {
 //! @brief Estimating the height of a building.

test/CMakeLists.txt

@@ -44,7 +44,8 @@ foreach(
   "kalman_format_arguments.cpp"
   "kalman_format_float_1x1x1.cpp"
   "kalman_format.cpp"
-  "kalman_println.cpp")
+  "kalman_println.cpp"
+  "printer_kf_1x1x0_building_height.cpp")
   get_filename_component(NAME ${TEST} NAME_WE)
   add_executable(kalman_test_${NAME}_driver ${TEST})
   target_link_libraries(kalman_test_${NAME}_driver PRIVATE kalman kalman_main

test/printer_kf_1x1x0_building_height.cpp

@@ -0,0 +1,76 @@
+#include "fcarouge/kalman.hpp"
+
+#include <cassert>
+#include <cmath>
+
+namespace fcarouge::sample {
+namespace {
+//! @brief Estimating the height of a building.
+//!
+//! @copyright This example is transcribed from KalmanFilter.NET copyright Alex
+//! Becker.
+//!
+//! @see https://www.kalmanfilter.net/kalman1d.html#ex5
+//!
+//! @details Assume that we would like to estimate the height of a building
+//! using a very imprecise altimeter. We know for sure, that the building height
+//! doesn’t change over time, at least during the short measurement process. The
+//! true building height is 50 meters. The altimeter measurement error (standard
+//! deviation) is 5 meters. The set of ten measurements is: 48.54m, 47.11m,
+//! 55.01m, 55.15m, 49.89m, 40.85m, 46.72m, 50.05m, 51.27m, 49.95m.
+//!
+//! @image html ./sample/image/kf_1x1x0_building_height.svg
+//!
+//! @example kf_1x1x0_building_height.cpp
+[[maybe_unused]] auto sample{[] {
+  // A one-dimensional filter, constant system dynamic model.
+  auto filter{
+      kalman{// One can estimate the building height simply by looking at it.
+             // The estimated state building height is: X = 60 meters.
+             state{60.},
+             // The building height measurement Z.
+             output<double>,
+             // A human’s estimation error (standard deviation) is about 15
+             // meters: σ = 15. Consequently the variance is σ^2 = 225. The
+             // estimate uncertainty is: P = 225.
+             estimate_uncertainty{225.},
+             // Since the standard deviation σ of the altimeter measurement
+             // error is 5, the variance σ^2 would be 25, thus the
+             // measurement, output uncertainty is: R = 25.
+             output_uncertainty{25.}} |
+      printer};
+
+  assert(60 == filter.x() &&
+         "Since our system's dynamic model is constant, i.e. the building "
+         "doesn't change its height: 60 meters.");
+  assert(225 == filter.p() &&
+         "The extrapolated estimate uncertainty (variance) also doesn't "
+         "change: 225");
+
+  // Now, we shall predict the next state based on the initialization values.
+  // Note: The prediction operation needs not be performed since the process
+  // noise covariance Q is null in this example.
+  // Measure and update: the first measurement is: z1 = 48.54m.
+  filter.update(48.54);
+
+  // And so on.
+  filter.update(47.11);
+  filter.update(55.01);
+  filter.update(55.15);
+  filter.update(49.89);
+  filter.update(40.85);
+  filter.update(46.72);
+  filter.update(50.05);
+  filter.update(51.27);
+  filter.update(49.95);
+
+  // After 10 measurements the filter estimates the height of the building
+  // at 49.57m.
+  assert(std::abs(1 - filter.x() / 49.57) < 0.001 &&
+         "After 10 measurement and update iterations, the building estimated "
+         "height is: 49.57m.");
+
+  return 0;
+}()};
+} // namespace
+} // namespace fcarouge::sample