On Wednesday, February 13, 2013 5:07:20 AM UTC+13, winnie wrote: > "aasim Azooz" <firstname.lastname@example.org> wrote in message <email@example.com>... > > > > > > if y=f(x) then the first derivative is > > > y1=diff(y)./diff(x) > > > The second derivative is > > > y2=diff(y1)./diff(x) > > > don't forget that the size of y1 is less than the size of y > > > by one and the size of y2 is less than the size of y by two > > > > > > Aasim Azooz > > > > > > > Hi, > > > > I just looked into computing an approximate second derivative with Matlab and found the answer given by Aasim (above). > > > > However, shouldn't it rather be: > > y2=diff(y1)./diff(x^2) ? > > > > The answer Aasim gave comes up repeatedly (in similar form) in my web searches, hence I am not sure whether I am making a conceptual error here... > > My x values are equally spaced, in case that makes a difference. > > > > Thanks, > > Winnie
Yes, you are making a conceptual error. Aasim has the correct algorithm.