Merge pull request #55 from jwnimmer-tri/roots

fixup! Implements symbolic::Polynomial::Roots()
RussTedrake · Sep 11, 2023 · 2582112 · 2582112
2 parents e47bc20 + 32057c7
commit 2582112
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Showing 2 changed files with 12 additions and 12 deletions.
diff --git a/common/symbolic/polynomial.cc b/common/symbolic/polynomial.cc
@@ -1056,9 +1056,9 @@ bool Polynomial::IsOdd() const {
 
 Eigen::VectorXcd Polynomial::Roots() const {
   if (indeterminates().size() != 1) {
-    throw std::runtime_error(fmt::format(
-        "{} is not a univariate polynomial; it has indeterminates {}.",
-        ToExpression().to_string(), indeterminates().to_string()));
+    throw runtime_error(fmt::format(
+        "{} is not a univariate polynomial; it has indeterminates {}.", *this,
+        indeterminates()));
   }
 
   // We find the roots by computing the eigenvalues of the companion matrix.
@@ -1074,11 +1074,11 @@ Eigen::VectorXcd Polynomial::Roots() const {
   double leading_coefficient = 0;
   for (const auto& [monomial, coeff] : monomial_to_coefficient_map()) {
     if (!is_constant(coeff)) {
-      throw std::runtime_error(
-          fmt::format("Polynomial::Roots() only supports polynomials with "
-                      "constant coefficients. This polynomial has coefficient "
-                      "{} for the monomial {}.",
-                      coeff.to_string(), monomial.ToExpression().to_string()));
+      throw runtime_error(fmt::format(
+          "Polynomial::Roots() only supports polynomials with constant "
+          "coefficients. This polynomial has coefficient {} for the "
+          "monomial {}.",
+          coeff, monomial));
     }
     const int power = monomial.total_degree();
     if (power == degree) {

diff --git a/common/symbolic/test/polynomial_test.cc b/common/symbolic/test/polynomial_test.cc
@@ -1512,7 +1512,7 @@ TEST_F(SymbolicPolynomialTest, Roots) {
 
   // Note: the order of the roots is not guaranteed. Sort them here by real,
   // then imaginary.
-  auto sort = [](const Eigen::VectorXcd& v) {
+  auto sorted = [](const Eigen::VectorXcd& v) {
     Eigen::VectorXcd v_sorted = v;
     std::sort(v_sorted.data(), v_sorted.data() + v_sorted.size(),
               [](const std::complex<double>& a, const std::complex<double>& b) {
@@ -1526,22 +1526,22 @@ TEST_F(SymbolicPolynomialTest, Roots) {
 
   // Include a repeated root.
   p = symbolic::Polynomial{(x_ - 1.23) * (x_ - 4.56) * (x_ - 4.56)};
-  roots = sort(p.Roots());
+  roots = sorted(p.Roots());
   EXPECT_TRUE(
       CompareMatrices(roots.real(), Eigen::Vector3d{1.23, 4.56, 4.56}, 1e-7));
   EXPECT_TRUE(CompareMatrices(roots.imag(), Eigen::Vector3d::Zero(), 1e-7));
 
   // Complex roots.  x^4 - 1 has roots {-1, -i, i, 1}.
   p = symbolic::Polynomial{pow(x_, 4) - 1};
-  roots = sort(p.Roots());
+  roots = sorted(p.Roots());
   EXPECT_TRUE(
       CompareMatrices(roots.real(), Eigen::Vector4d{-1, 0, 0, 1}, 1e-7));
   EXPECT_TRUE(
       CompareMatrices(roots.imag(), Eigen::Vector4d{0, -1, 1, 0}, 1e-7));
 
   // Leading coefficient is not 1.
   p = symbolic::Polynomial{(2.1 * x_ - 1.23) * (x_ - 4.56)};
-  roots = sort(p.Roots());
+  roots = sorted(p.Roots());
   EXPECT_TRUE(
       CompareMatrices(roots.real(), Eigen::Vector2d{1.23 / 2.1, 4.56}, 1e-7));
   EXPECT_TRUE(CompareMatrices(roots.imag(), Eigen::Vector2d::Zero(), 1e-7));