Solving system of 3 quadratic equations!

  • #1
Gbl911
18
0
Given the following equation:

R = ((Q-P) / |Q-P|) ⋅ V
where Q, P, and V are 3 dimensional vectors, R is a scalar, "" denotes the dot product, and |Q-P| is the magnitude of Q-P.

Assuming Q, V, and R are known and given 3 independent equations with different values for Q, V, and R that all correspond to one vector P, solve for all elements of P.

As an example the first equation would be:
R1 = ((Q1-P) / |Q1-P|) ⋅ V1

Expanding this out to view individual elements yields:
R1 = ((Q11-P1)V11 + (Q12-P2)V12 + (Q13-P3)V13) / sqrt((Q11-P1)2 + (Q12-P2)2+ (Q13-P3)2)

From here I have gotten some of the way through solving the 3 equations by substitution but it becomes unbearably long and requires the quadratic equation due to the sqrt... I have also tried using every numerical method I know to solve it but it seems the equation is far to ill conditioned and gradient methods are almost useless. I haven't found anything online regarding it and was hoping some of you who are good at math would be able to give me some guidance. I'm hoping there is a way without having to go through the substitution by hand but I may end up just doing that....
 
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  • #2
[tex]\mathbf{v}\cdot\frac{\mathbf{P}-\mathbf{Q}}{|\mathbf{P}-\mathbf{Q}|}=1[/tex]where
[tex]\mathbf{v}=\frac{\mathbf{V}}{R}[/tex]
the equations are
[tex]\sum_{k=1}^3 v_{ik}(p_k-q_{ik})=\sqrt{\sum_{k=1}^3(p_k-q_{ik})^2}[/tex]
for i=1,2,3. With ##\{q_{ik}\}## and ##\{v_{ik}\}## given, you expect to decide ##(p_1,p_2,p_3)## as cross point of three 3D quadratic surfaces.
 
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