# [Fwd: Re: Difference between 2 lines and adaptative grid] Classic List Threaded 1 message Reply | Threaded
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## [Fwd: Re: Difference between 2 lines and adaptative grid]

 On Mon, 2005-08-29 at 17:39 +0200, Nicolas Girard wrote: > Hi all, > > I apologize for beeing slightly off-topic with this question, but I couldn't > think about a better place to ask :-/ > > Consider two vectors x1 and y1. Using matplotlib, plot(x1,y1) will display the > line joining all points whose coordinates are (x1(i),y1(i)) > Now, consider another couple of vectors x2 and y2. > Using plot(x1,y1,x2,y2) we are shown the 2 lines corresponding to (x1,y1) and > (x2,y2), and we can compare these two lines with the naked eye > > My question is, how to do this quantitatively ? Is there a way of calculating > the difference between the two sets of points, and then plot this difference, > using matplotlib ? I mean, if the data was generated using a fixed grid, it > would be enough to plot (y2-y1) but with an adaptative grid, x1 and x2 > differ. Do you know about a quick & dirty way to achieve this ? You have to interpolate the results to a common vector, and then perform the difference. If you want to reproduce exactly the difference you can see on-screen, then use a linear interpolation (cause the lines joining successive points are straight, hence a linear interpolation -  well, assuming that your plot is in cartesian coordinates, else this becomes more tricky), and map both set of results to the common vector (list(x1)+list(x2)).sort() (remove duplicated values and reduce it to the interval max(min(x1),min(x2)), min(max(x1),max(x2)) if you want to be clean and safe...) ------------------------------------------------------- SF.Net email is Sponsored by the Better Software Conference & EXPO September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf_______________________________________________ Matplotlib-users mailing list [hidden email] https://lists.sourceforge.net/lists/listinfo/matplotlib-users