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# Curve Equation

## Curve Equation

Can I draw a curve, and get Mathcad to predict its equation!!!!

5-Regular Member

What data are you planning on drawing the curve from?

I'm sure you could spline the data and work with it.

Mike

24-Ruby III
5-Regular Member

Valery,

Mike

4-Participant

I literally want to draw a curve on a paper, and get Mathcad to predict the equation!!

5-Regular Member

Then you would have to trace the graph, Valery passed an excellent tool for this and extract the data that way.

I can't see any other way of achieving it.

Mike

19-Tanzanite
 I literally want to draw a curve on a paper, and get Mathcad to predict the equation!!

That is not possible. Not for Mathcad, not for any software. If you have data that represents a curve and you already know the functional form of the curve, but not the parameters, then in principle you can find the parameters. For example, you might know it's quadratic, in which case you can fit a quadratic to the data to find the coefficients. There is no software that can tell you it's a quadratic though. You could also fit a general interpolating function to the curve, for example a cubic spline. That's not "the" equation of the curve though, it's just an equation that passes through the known points.

24-Ruby II

Provide this curve.

1-Newbie

i know a software named 1stOpt can do this,but the data must have only one independent variable，that means f(x),not f(x,y),f(x,y,z).... you may ask how it works,the theory is simple.it has storaged many functions，exponential, logarithmic, trigonometric...then you enter your data，it fit the data using more than 3000 functions，at last,you can pick up the function that fit the data best.

the version of this software is in chinese,

you also can try to use this software attached.

24-Ruby II
 赵亚军 wrote:...the version of this software is in chinese...

The English version is available?

1-Newbie

Mike,

I have never tried this but often wondered .. what if I drew a curve on a piece of paper and scanned it, then brought the scan in as a bit map. Now use the imaging function binarize, turning the scanned image into a white uniform grid with black data points representing the curve. In line programming could allow me to loop thru rows/cols, when image/matrix value is 0 (black) I get x,y from row.col. Then I just use regression/curve fitting to get the equation.

What am I missing? Why will this not work?

John

19-Tanzanite
 Then I just use regression/curve fitting to get the equation. What am I missing? Why will this not work?

You don't know the functional form of "the" equation. You can guess a form, and fit that to the curve. If your guessed function has fewer parameters than there are data points you will not get an exact fit though, unkess by some small miracle you actually did guess "the" equation. Or you could use interpolation, for example a cubic spline, which will pass through every point, but is that "the" equation?

1-Newbie

ahh got it. I was thinking of psplining the points ... but that is really not the equation , although it may look nice. Thanks

19-Tanzanite
 although it may look nice.

Or sometimes not

And if the curve is multivalued in both x and y then a cubic spline will not work. A parametric spline will of course, but then you don't even have an equation, you have two equations in an independent variable.

And what if I draw both a vertical line and a horizontal line as part of my curve? Then it is undefined at one point in both dimesions.

Community Manager
Status changed to: Archived

Hello,

We are archiving your idea as part of a general review. This action is based on the age of your idea and the total number of votes received, as per this announcement.

You can always post a new idea with all the details required in the form.