I appreciate your honesty, but this is not a forum for getting your homework done. There is a reason why your professor assigns homework, which is for you to learn. By getting us to solve your homework problems, you are defeating that purpose, and more importantly, you are wasting your time, your professor's time, and our time.
You are more likely to get help, if you told us what approaches you had tried, and the problems that you had encountered. Hope this is helpful, Ravi. -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of cr...@sharkdefense.com Sent: Friday, October 08, 2010 2:26 PM To: r-help@r-project.org Subject: [R] Trapezoid Rule Dear R Users, I've never used R before and my professor has asked us to do some pretty intense programming (or it's intense to me at least). Here is the question: Modify the function myquadrature inside the script so that it returns the quadrature of descrete data using the trapezoidal rule. Modify the call to the function at the bottom of the script so that is uses your modifies routine to compute the total volume flux through a transect using descrete observations of bathymetry and vertically-averaged velocity. The professor supplied us with some sample code and i'm pretty sure it outlines the whole problem. My issue is, I have no idea how to write the sum code for the trapezoid rule to estimate the area under the curve: Here is the code provided: myquadrature = function(f,a,b) { # user-defined quadrature function # integrate data f from x=a to x=b assuming f is equally spaced over the interval # use type # determine number of data points npts = length(f) nint = npts -1 #number of intervals if(npts <=1) error('need at least two points to integrate') end; # set the grid spacing if(b <=a) error('something wrong with the interval, b should be greater than a') else dx = b/real(nint) end; # trapezoidal rule # can code in line, hint: sum of f is sum(f) # f[1] is the first entry in f } # velocity profile across a channel # remember to use ? for help, e.g. ?seq x = seq(0,2000,10) # you can access one element of a list of values using brackets # x[1] is the first x value, x[2], the 2nd, etc. # if you want the last value, a trick is x[length(x)] # this works because length(x) returns the number of values in the series # the function cos is cosine and mean gives the mean value # pi is 3.1415, or pi h = 10.*(cos(((2*pi)/2000)*(x-mean(x)))+1) #depth u = 1.*(cos(((2*pi)/2000)*(x-mean(x)))+1) #vertically-averaged cross-transect velocity # set begin and end points for the integration a = x[1] b = x[length(x)] # call your quadrature function. Hint, the answer should be 30000. print(myquadrature()) Any assistance with this problem would be greatly appreciated. Thanks, Casey ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
