Field: Calculus
Image Created By: Mathematica
Website: Mathematica

This image shows a surface known as a monkey saddle.

# Basic Description

The monkey saddle is a surface in Multivariable Calculus that belongs to the class of saddle surfaces. The surface gets its name from the fact that it has three depressions like a saddle for a monkey, which would require two depressions for the legs and one for the monkey's tail.

# A More Mathematical Explanation

Note: understanding of this explanation requires: *Calculus

### Expressions Defining the Surface

The monkey saddle is defined, in '"`UNIQ--balloon-00000000-Q [...]

### Expressions Defining the Surface

The monkey saddle is defined, in , by the equation: $z(x,y)$ $=x^2$ $3 x y^2$

It can also be described by the parametric equations: $x(u,v)=u$ $y(u,v)=v$ $z(u,v)=u^2 - 3xy^2$

The point (0,0,0) corresponds to a degenerate critical point of the function z(x,y) at (0,0). It is the surface's only stationary point, or point where the derivative of the function is zero. This point is also a saddle point, a point on the surface which is a stationary point, but not an extremum.

### Fundamental Forms

The coefficients of the first fundamental form of the monkey saddle are given by: $E = 1 + 9(u^2 + v+2)^2$ $F = -18uv(u^2-v^2)$ $G = 1+36u^2v^2$

And the coefficients of the second fundamental form of the monkey saddle are: $e = \frac{(6u)}{(\sqrt{1+9(u^2+v^2)^2})}$ $f = \frac{-(6v)}{(\sqrt{1+9(u^2+v^2)^2})}$ $g = \frac{-(6u)}{(\sqrt{1+9(u^2+v^2)^2})}$

#### Area Element

Thus, the area element of the monkey saddle is given by: $dA=\sqrt{EG-F^2}du \wedge dv = \sqrt{1+9(u^2+v^2)^2}du \wedge dv$

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