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v2009.01.01 - Convex Optimization

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366 CHAPTER 5. EUCLIDEAN DISTANCE MATRIX<br />

(a)<br />

(c)<br />

x 3<br />

x 4 x 5<br />

x 5 x 6<br />

√<br />

d13√d14<br />

x 3<br />

ˇx 3 ˇx 4<br />

√<br />

d12<br />

ˇx 2<br />

x 1<br />

x 1<br />

x 2<br />

x 4<br />

x 1<br />

x 1<br />

Figure 97: (a) Given three distances indicated with absolute point<br />

positions ˇx 2 , ˇx 3 , ˇx 4 known and noncollinear, absolute position of x 1 in R 2<br />

can be precisely and uniquely determined by trilateration; solution to a<br />

system of nonlinear equations. Dimensionless EDM graphs (b) (c) (d)<br />

represent EDMs in various states of completion. Line segments represent<br />

known absolute distances and may cross without vertex at intersection.<br />

(b) Four-point list must always be embeddable in affine subset having<br />

dimension rankVN TDV N not exceeding 3. To determine relative position of<br />

x 2 ,x 3 ,x 4 , triangle inequality is necessary and sufficient (5.14.1). Knowing<br />

all distance information, then (by injectivity of D (5.6)) point position x 1<br />

is uniquely determined to within an isometry in any dimension. (c) When<br />

fifth point is introduced, only distances to x 3 ,x 4 ,x 5 are required to<br />

determine relative position of x 2 in R 2 . Graph represents first instance<br />

of missing distance information; √ d 12 . (d) Three distances are absent<br />

( √ d 12 , √ d 13 , √ d 23 ) from complete set of interpoint distances, yet unique<br />

isometric reconstruction (5.4.2.2.6) of six points in R 2 is certain.<br />

(b)<br />

(d)

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