What the Hessian tells you

The Hessian matrix collects every second-order partial derivative of ff.

Diagonal entries measure curvature along each axis, while off-diagonal entries measure how variables interact through mixed partial derivatives.

In optimization, the Hessian helps classify critical points and understand whether a surface bends upward, downward, or in mixed directions.

Input tips

  • Separate variables with commas, such as x, y or x, y, z.
  • Use math syntax like x^2*y + y^3 or exp(x*y).
  • If the function is twice continuously differentiable, the Hessian is typically symmetric.