# What is Hessian?

I was working today and had to calculate the Hessian of a matrix, then I wondered a Hessian function might already exist. I typed Hessian and it does exist, but there's no documentation (neither online nor software embedded) that explains what the heck this function is. ?Hessian confirms the tag is protected and that it must do something. I'm curious now... Does anyone know what's going on?

P.S.: I'm using Mathematica 10.

P.S.2: I know how to calculate an Hessian.

• Maybe it is a function that will be included in later versions (or has already been included in some 10.x version?). At the moment there is the name... Aug 29, 2016 at 19:12
• No predefined function. Assuming your function f is a function of a vector (i.e., f[x1, x2, ..., xn] use D[f[x1, x2, ...,xn], {{x1, x2, ..., xn}, 2}] Aug 29, 2016 at 19:17
• Thanks, but defining a function for calculating an Hessian was never the problem. I was interested in the existence of a phantom function I found by accident =) Aug 29, 2016 at 19:18
• Apart for simply being a Protected symbol, PrintDefinitions (from GeneralUtilities package) shows no other definitions attached to it (not even <<kernel function>>). So it does nothing. Aug 29, 2016 at 19:52
• Hessian (alternatively "Hessian") is an option name. Related: (91628), (98501), Newton's method tutorial, derivative tutorial Aug 30, 2016 at 12:30

The Mathematica documentation for FindMaxValue includes the example
FindMaxValue[Sin[x] Sin[2 y], {x, y},

which includes a reference to Hessian as part of the Method`. I believe that this (and probably other similar usages) will cause it to appear as a symbol in the "System" context.