Monday, January 7, 2013

Signed Distance Function

Introduction to signed distance function:

The signed distance function is of a set S in the metric space that determines how the given the point x is close to the boundary of set S with the point x is inside S means the function having the positive values, it decreases in value as x approaches the boundary of S where the signed distance function is zero, and the point x having negative values outside of S. I like to share this Rules of Differentiation with you all through my article.

Formula for Signed Distance Function:

If the point (X, d) is a metric space means the signed distance function f is ,

`g(x)={b(x,s^c) if x in S,-b(x,S) if x in S^(c):}`

where

`b(x,S)=("inf"_(y in S))( b(x,y))`

here 'inf' represents the infimum or the greatest lower bound of a subset S.If S is denoted a subset of the Euclidean space Rn with piecewise smooth boundary, the signed distance function is differentiable, and its gradient(`grad`)satisfies the non linear partial differential equation that is eikonal equation.

`|grad g|=1`

The form of the eikonal equation is

`|grad u(x)|= G(x) ,x in Omega`

It is subject to `u|_(del Omega)=0` , where Ω is an open set in with well behaved boundary, G(x) is a function and having the positive values,  `grad` is the gradient. In some case when Fg= 1, the solution gives the signed distance function from `del Omega.`

Example 1 for Signed Distance Function :

Solve `G(x)={x^2y ,if x =1 ; y=1` using signed distance function.

Solution:

`|grad g|=1`

The formula is

`grad g= (del g)/(del x) +(del g)/(del y)`

`(del g)/(del x)=2xy`    ; `(del g)/(del y)=x^2(1)=x^2`

subsitute x=1 and y=1 and we get,

`grad g= (del g)/(del x) +(del g)/(del y)`

=2(1)(!)+(1)^2

=2+1=3

The result is  `|grad g|=3`

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Example 2 for Signed Distance Function :

Solve `G(x)={x^2 +y^2 if x=1,y=1 ` using signed distance function.

Solution:

`|grad g|=1`

The formula is

`grad g= (del g)/(del x) +(del g)/(del y)`

`(del g)/(del x)=2x`    ; `(del g)/(del y)=2y`

subsitute x=1 and y=1 and we get,

`grad g= (del g)/(del x) +(del g)/(del y)`

=2(1)+2(1)

=2+2=4

The result is  `|grad g|=4`

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