cancel
Showing results for
Did you mean:
cancel
Showing results for
Did you mean:

Community Tip - Visit the PTCooler (the community lounge) to get to know your fellow community members and check out some of Dale's Friday Humor posts! X

3-Visitor

## Inverse function based or cordinates

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.

1 ACCEPTED SOLUTION

Accepted Solutions
23-Emerald III
(To:retvigkasper)

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)

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

6 REPLIES 6
3-Visitor
(To:retvigkasper)

23-Emerald III
(To:retvigkasper)

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

23-Emerald III
(To:retvigkasper)

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:

(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!):

(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

3-Visitor
(To:LucMeekes)

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 😞

23-Emerald III
(To:retvigkasper)

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)

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

3-Visitor
(To:LucMeekes)

Sweat.... you nailed it 😄 thanks a lot

Announcements
Top Tags