Move lowpass filter code to header and fix comment

CMakeLists.txt

@@ -53,7 +53,6 @@ add_library(franka SHARED
   src/load_calculations.cpp
   src/log.cpp
   src/logger.cpp
-  src/lowpass_filter.cpp
   src/model.cpp
   src/model_library.cpp
   src/network.cpp

include/franka/lowpass_filter.h

@@ -2,6 +2,8 @@
 // Use of this source code is governed by the Apache-2.0 license, see LICENSE
 #pragma once
 
+#include <cmath>
+
 /**
  * @file lowpass_filter.h
  * Contains functions for filtering signals with a low-pass filter.
@@ -26,6 +28,9 @@ constexpr double kDefaultCutoffFrequency = 100.0;
  *
  * @return Filtered value.
  */
-double lowpassFilter(double sample_time, double y, double y_last, double cutoff_frequency);
+inline double lowpassFilter(double sample_time, double y, double y_last, double cutoff_frequency) {
+  double gain = sample_time / (sample_time + (1.0 / (2.0 * M_PI * cutoff_frequency)));
+  return gain * y + (1 - gain) * y_last;
+}
 
 }  // namespace franka

include/franka/robot.h

@@ -135,6 +135,7 @@ class Robot {
    * This could distort your motion!
    * @param[in] cutoff_frequency Cutoff frequency for a first order lowpass filter applied on
    * the user commanded signal.
+   *
    * @throw ControlException if an error related to torque control or motion generation occurred.
    * @throw InvalidOperationException if a conflicting operation is already running.
    * @throw NetworkException if the connection is lost, e.g. after a timeout.

test/control_loop_tests.cpp

@@ -5,8 +5,8 @@
 
 #include <gmock/gmock.h>
 
+#include <franka/lowpass_filter.h>
 #include "control_loop.h"
-#include "franka/lowpass_filter.h"
 #include "motion_generator_traits.h"
 
 #include "helpers.h"