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FP_101198334-Participant
4-Participant
November 25, 2021
Solved

Root finding of vector function using find

  • November 25, 2021
  • 2 replies
  • 2919 views

Hello everyone

 

I have been a bit puzzled by the error I get when using find with vector variables. I have defined a triangle DEF in 2 dimensions. I am searching for the coordinates of a 4th point S such that the sum of vectors from S to the other points is a zero vector (weighed with parameters g and t). Unfortunately, find does not find a solution.

I thought maybe it was due to a divide by zero error, but adding the constraint that the product of the norms must be strictly positive does not solve the problem. The initial guess is already fairly close to the solution, so I don't believe it is the issue.

I have attached the mcdx file as well as a screenshot for convenience. Any idea of what is going wrong ?

2021-11-25_095543.png

 

François

 

Best answer by Werner_E
The initial guess is already fairly close to the solution

I wouldn't call that "close":

Werner_E_0-1637842800335.png

 

I don't think that your equation has solution!

I am not sure about the properties you demand for your points S and suggest that you check your equation.

 

Using "minerr" gives us a  "solution" very close to point F but there seems to be no solution which fulfills the equation to 100%

Werner_E_1-1637842890375.png

 

2 replies

V
VladimirN24-Ruby III
24-Ruby III
November 25, 2021

One of the possible solutions in the attachment.

W
Werner_E25-Diamond I
25-Diamond I
November 25, 2021

The x= mean of the three points wasn't meant as an additional condition but was the guess value! 🙂

V
VladimirN24-Ruby III
24-Ruby III
November 25, 2021

I slightly changed the conditions of the problem and used it as an example 🙂.

W
Werner_E25-Diamond IAnswer
25-Diamond I
November 25, 2021
The initial guess is already fairly close to the solution

I wouldn't call that "close":

Werner_E_0-1637842800335.png

 

I don't think that your equation has solution!

I am not sure about the properties you demand for your points S and suggest that you check your equation.

 

Using "minerr" gives us a  "solution" very close to point F but there seems to be no solution which fulfills the equation to 100%

Werner_E_1-1637842890375.png

 

    F
    FP_101198334-ParticipantAuthor
    4-Participant
    November 25, 2021

    Thank you Werner and Vladimir for suggesting the use of minerr.

    Since S has to be inside the triangle DEF, using the centroid seems a good enough guess without further info. That's what I meant by fairly close. In fact Werner's suspicion is correct that the problem simply has no solution with the proposed set of parameters g, t. For instance, changing g from 200 to 400 does work. That will teach me about trying to validate a program with no physical solutions ! 😅

    I will try to improve the sheet so that it correctly returns no solution, rather than the error. There again minerr seem to come handy.

    Thank you for the swift support !

     

     

     

      V
      VladimirN24-Ruby III
      24-Ruby III
      November 25, 2021

      You're welcome.

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