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retvigkasper1-Visitor
1-Visitor
November 28, 2017
Solved

Inverse function based or cordinates

  • November 28, 2017
  • 2 replies
  • 3168 views

Hello

 

I have 42 x and y variables where an regression are made. Now i need make an reverse function of this. How and can some help + explain how it is done so i can make it by myself in the future !!!

  

Thanks


Regards.

Best answer by LucMeekes

Ah, you need a little more than the inverse. You want your function mirrored over a line.

Here's how to do it for a straight line through 0,0:

(I did this in Mathcad, not Prime; you should be able to recreate it in Prime)

LM_20171129_Mirror.png

 

There's one extra parameter (p) to the mirror line function m. You can play with that and see how the results change.

 

Success!
Luc

2 replies

R
retvigkasper1-VisitorAuthor
1-Visitor
November 28, 2017

File cant be uploaded so an google drive link here.

 

https://drive.google.com/open?id=1Z1w0hKn-I5gotgrn3dEq7ZeFJoe5JRef

L
LucMeekes23-Emerald IV
23-Emerald IV
November 28, 2017

To attach your worksheet:

There's a bug on this forum that often causes a failure to attach a worksheet. You then need to ZIP it first.

To zip, in Windows explorer select the worksheet file, then with the right-mous button select 'Send to'=> 'compressed (zipped) folder' the resulting .zip file can be attached.

 

Success!
Luc

L
LucMeekes23-Emerald IV
23-Emerald IV
November 28, 2017

Now to your question.

Since you know the forward function, to get the inverse function you can try to solve for x with known value of y, either symbolically or numerically.

Since it's a 4th order function, you won't like the symbolic solution, if Prime is willing to provide it at all.

(I'm limited to Express Prime = no symbolics) Here's a small part of the results using Mathcad 11:

LM_20171128_InverseSymbolic.png

(Note that:

- I've made sure that all constants are integers, to prevent extremely wide real numbers, by multiplying both sides of the equation with 100.

- This picture shows only a small part of two of the four possible solutions. And most probably only one, or two of the solutions give real answers; the others giving complex answers. )

 

Another way that even works in Express Prime is to use the root function (look it up in the help!):

LM_20171128_Inverse.png

(I've set the upper limit for x-values to 11, to assure that all values are found on the defined part of the graph. If you need larger x due to larger y, just increase that value above 11)

Success!
Luc

R
retvigkasper1-VisitorAuthor
1-Visitor
November 29, 2017

Mabi i explayned myself a bit wrong. I uploaded a new file with a paint picture of how it shud look like. I tryed the inv function and dosent help me, with the thing i want 😞 

L
LucMeekes23-Emerald IVAnswer
23-Emerald IV
November 29, 2017

Ah, you need a little more than the inverse. You want your function mirrored over a line.

Here's how to do it for a straight line through 0,0:

(I did this in Mathcad, not Prime; you should be able to recreate it in Prime)

LM_20171129_Mirror.png

 

There's one extra parameter (p) to the mirror line function m. You can play with that and see how the results change.

 

Success!
Luc

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