These are things named after Jacques Hadamard (1865–1963), a French mathematician. (For references, see the respective articles.)
Theorems, lemmas, and conjectures
Many of these results are sometimes called "Hadamard's theorem".
- Cartan–Hadamard theorem, a statement in Riemannian geometry concerning the structure of complete Riemannian manifolds of non-positive sectional curvature
- Cartan–Hadamard conjecture, an open problem in Riemannian geometry and geometric measure theory concerning the generalization of the classical isoperimetric inequality to spaces of nonpositive sectional curvature
- Cauchy–Hadamard theorem, a statement in complex analysis describing the radius of convergence of a power series
- Hadamard's inequality, a bound on the determinant of a matrix whose entries are complex numbers in terms of the lengths of its column vectors
- Hermite–Hadamard inequality, a bound on the mean value of a convex function in an interval in terms of the value it takes at the mid-point and ends of interval
- Hadamard's lemma, a result closely related to the first-order term in Taylor's theorem
- Ostrowski–Hadamard gap theorem concerning the analytic continuation of complex power series
- Hadamard three-circle theorem, concerning the maxima of holomorphic functions within concentric circles in the complex plane.
- Hadamard three-lines theorem, concerning the maxima of holomorphic functions defined in regions bounded by parallel lines in the complex plane.
- Hadamard's embedding theorem [ru]
Mathematical objects and definitions
- Hadamard product:
- entry-wise matrix multiplication
- an infinite product expansion for the Riemann zeta function
- Hadamard code
- Hadamard's dynamical system
- Hadamard manifold
- Hadamard matrix
- Hadamard space
- Hadamard Transform and Hadamard gate
- Hadamard variance
- Hadamard's gamma function
Equations, problems, and methods
- Hadamard–Rybczynski equation
- Hadamard's maximal determinant problem
- Hadamard's method of descent
- Hadamard regularization