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tools/sysid/src/main/native/cpp/analysis/FeedbackAnalysis.cpp

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+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "sysid/analysis/FeedbackAnalysis.h"
+
+#include <cmath>
+
+#include <frc/controller/LinearQuadraticRegulator.h>
+#include <frc/system/LinearSystem.h>
+#include <frc/system/plant/LinearSystemId.h>
+#include <units/acceleration.h>
+#include <units/velocity.h>
+#include <units/voltage.h>
+
+#include "sysid/analysis/FeedbackControllerPreset.h"
+
+using namespace sysid;
+
+using Kv_t = decltype(1_V / 1_mps);
+using Ka_t = decltype(1_V / 1_mps_sq);
+using Matrix1d = Eigen::Matrix<double, 1, 1>;
+
+FeedbackGains sysid::CalculatePositionFeedbackGains(
+    const FeedbackControllerPreset& preset, const LQRParameters& params,
+    double Kv, double Ka) {
+  if (!std::isfinite(Kv) || !std::isfinite(Ka)) {
+    return {0.0, 0.0};
+  }
+
+  // If acceleration for position control requires no effort, velocity becomes
+  // an input. We choose an appropriate model in this case to avoid numerical
+  // instabilities in the LQR.
+  if (std::abs(Ka) < 1e-7) {
+    // System has position state and velocity input
+    frc::LinearSystem<1, 1, 1> system{Matrix1d{0.0}, Matrix1d{1.0},
+                                      Matrix1d{1.0}, Matrix1d{0.0}};
+
+    frc::LinearQuadraticRegulator<1, 1> controller{
+        system, {params.qp}, {params.r}, preset.period};
+    controller.LatencyCompensate(system, preset.period,
+                                 preset.measurementDelay);
+
+    return {Kv * controller.K(0, 0) * preset.outputConversionFactor, 0.0};
+  }
+
+  auto system = frc::LinearSystemId::IdentifyPositionSystem<units::meters>(
+      Kv_t{Kv}, Ka_t{Ka});
+
+  frc::LinearQuadraticRegulator<2, 1> controller{
+      system, {params.qp, params.qv}, {params.r}, preset.period};
+  controller.LatencyCompensate(system, preset.period, preset.measurementDelay);
+
+  return {controller.K(0, 0) * preset.outputConversionFactor,
+          controller.K(0, 1) * preset.outputConversionFactor /
+              (preset.normalized ? 1 : units::second_t{preset.period}.value())};
+}
+
+FeedbackGains sysid::CalculateVelocityFeedbackGains(
+    const FeedbackControllerPreset& preset, const LQRParameters& params,
+    double Kv, double Ka, double encFactor) {
+  if (!std::isfinite(Kv) || !std::isfinite(Ka)) {
+    return {0.0, 0.0};
+  }
+
+  // If acceleration for velocity control requires no effort, the feedback
+  // control gains approach zero. We special-case it here to avoid numerical
+  // instabilities in LQR.
+  if (std::abs(Ka) < 1E-7) {
+    return {0.0, 0.0};
+  }
+
+  auto system = frc::LinearSystemId::IdentifyVelocitySystem<units::meters>(
+      Kv_t{Kv}, Ka_t{Ka});
+  frc::LinearQuadraticRegulator<1, 1> controller{
+      system, {params.qv}, {params.r}, preset.period};
+  controller.LatencyCompensate(system, preset.period, preset.measurementDelay);
+
+  return {controller.K(0, 0) * preset.outputConversionFactor /
+              (preset.outputVelocityTimeFactor * encFactor),
+          0.0};
+}