Graduate Civil Engineering Student

I have a really trivial question, is it possible for MATLAB to trace a line or a curve and recreate its mathematical equation? We use very complicated old charts from the 1960s that have no data, and have to interpolate giving recurring errors and inconsistent results.

My question is basically this, is is possible to trace the curves via some computer program and have matlab convert it into an equation?

[Andrew Newell]

This is an interesting question. Could you edit it to provide a more meaningful title?

[Hazim]

Andrew, elaborate on your comment more please, I would love to have this question help people with similar problems as mine

[Oleg Komarov]

Change the title of your thread to something related to question rather than leaving "Graduate Civil Engineering Student"

Answer 1

[bym]

try this from the file exchange

http://www.mathworks.com/matlabcentral/fileexchange/4316-reverseplot

Answer 2

[Walter Roberson]

There is the Curve Fitting Toolbox.

Generally speaking, if you do not have a good idea of what the form of the equation is, then you cannot determine the equation with any certainty: there are an infinite number of equations that fit any given set of data points perfectly. Indeed, if you get a perfect fit, chances are that you have over-fit.

Answer 3

[Kevin O'Hara]

(duplicate information)

Answer 4

[Kevin O'Hara]

MatLab has two function to create a curve through your data. [r1,m1,b1] = regression(xydata1(:,1)',xydata1(:,3)') and p1 = polyfit(xydata1(:,1)',xydata1(:,3)',2);

The coefficients m1 and b1 can be used for linear plots and the equation, whereas, p1 has the coefficients for a 2 or 3 or 4th order polynomial. I am using a 2nd order. See MatLab help function for more info on regression and ployfit functions.

Answer 5

[Hazim]

Thanks you guys, I think the combination of grabit and the reverseplot really helped me out.

I wish there was a way to show u the graphs i had to deal with. Using reverseplot

I dont know if the matlab functions wouldve worked as efficiently as I wanted, specially that the graph is on logscales. If anyone is familar with reverseplot or grabit, do you guys think there is a revamped code written out there?