Add ArcTanLoss, TolerantLoss and ComposedLossFunction.
Based on work by James Roseborough.
Change-Id: Idc4e0b099028f67702bfc7fe3e43dbd96b6f9256
diff --git a/internal/ceres/loss_function.cc b/internal/ceres/loss_function.cc
index 00b2b18..b948f28 100644
--- a/internal/ceres/loss_function.cc
+++ b/internal/ceres/loss_function.cc
@@ -77,6 +77,70 @@
rho[2] = - c_ * (inv * inv);
}
+void ArctanLoss::Evaluate(double s, double rho[3]) const {
+ const double sum = 1 + s * s * b_;
+ const double inv = 1 / sum;
+ // 'sum' and 'inv' are always positive.
+ rho[0] = a_ * atan2(s, a_);
+ rho[1] = inv;
+ rho[2] = -2 * s * b_ * (inv * inv);
+}
+
+TolerantLoss::TolerantLoss(double a, double b)
+ : a_(a),
+ b_(b),
+ c_(b * log(1.0 + exp(-a / b))) {
+ CHECK_GE(a, 0.0);
+ CHECK_GT(b, 0.0);
+}
+
+void TolerantLoss::Evaluate(double s, double rho[3]) const {
+ const double x = (s - a_) / b_;
+ // The basic equation is rho[0] = b ln(1 + e^x). However, if e^x is too
+ // large, it will overflow. Since numerically 1 + e^x == e^x when the
+ // x is greater than about ln(2^53) for doubles, beyond this threshold
+ // we substitute x for ln(1 + e^x) as a numerically equivalent approximation.
+ static const double kLog2Pow53 = 36.7; // ln(MathLimits<double>::kEpsilon).
+ if (x > kLog2Pow53) {
+ rho[0] = s - a_ - c_;
+ rho[1] = 1.0;
+ rho[2] = 0.0;
+ } else {
+ const double e_x = exp(x);
+ rho[0] = b_ * log(1.0 + e_x) - c_;
+ rho[1] = e_x / (1.0 + e_x);
+ rho[2] = 0.5 / (b_ * (1.0 + cosh(x)));
+ }
+}
+
+ComposedLoss::ComposedLoss(const LossFunction* f, Ownership ownership_f,
+ const LossFunction* g, Ownership ownership_g)
+ : f_(CHECK_NOTNULL(f)),
+ g_(CHECK_NOTNULL(g)),
+ ownership_f_(ownership_f),
+ ownership_g_(ownership_g) {
+}
+
+ComposedLoss::~ComposedLoss() {
+ if (ownership_f_ == DO_NOT_TAKE_OWNERSHIP) {
+ f_.release();
+ }
+ if (ownership_g_ == DO_NOT_TAKE_OWNERSHIP) {
+ g_.release();
+ }
+}
+
+void ComposedLoss::Evaluate(double s, double rho[3]) const {
+ double rho_f[3], rho_g[3];
+ g_->Evaluate(s, rho_g);
+ f_->Evaluate(rho_g[0], rho_f);
+ rho[0] = rho_f[0];
+ // f'(g(s)) * g'(s).
+ rho[1] = rho_f[1] * rho_g[1];
+ // f''(g(s)) * g'(s) * g'(s) + f'(g(s)) * g''(s).
+ rho[2] = rho_f[2] * rho_g[1] * rho_g[1] + rho_f[1] * rho_g[2];
+}
+
void ScaledLoss::Evaluate(double s, double rho[3]) const {
if (rho_.get() == NULL) {
rho[0] = a_ * s;
