Solving system of equations with 3 unknowns

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Swasti Khuntia
Swasti Khuntia il 16 Ott 2012
Hello All,
I'm extracting points from a graph. I'll be using those points to find three unknowns from the equation of the form ax+by+cz = d.
If I'm extracting 3 points, then I can solve as simultaneous equations with 3 unknowns [AX=B form, Cramers's Rule]. But if I extract more than 3 points, how to solve?

Risposte (2)

Matt J
Matt J il 16 Ott 2012
Whether with 3 or more than 3 variables, you will obtain an equation of the form
A*X=B
and you would solve it by doing X=A\B. There is no need to use Cramer's rule (and it's probably not a good idea).
  4 Commenti
Swasti Khuntia
Swasti Khuntia il 16 Ott 2012
Thanks a lot. I found the solution using pinv function.
Matt J
Matt J il 16 Ott 2012
No, it's a bad solution. X=A\B is much more efficient.

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Swasti Khuntia
Swasti Khuntia il 17 Ott 2012
But in my case, pinv is the only solution.
  1 Commento
Matt J
Matt J il 17 Ott 2012
That would have to mean that you are not selecting enough linear independent points (2 or less). That raises the question as to why you don't just stop selecting after you have 2 points. That also raises the question as to how you hope to get a good fit to your parameters when you have fewer independent data points than parameters.

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