Riemann Sums; how to input interval as well as function f(x)?

%I have not visited this function in a while and can not see why it is not working. no matter what I use for 'n', it says it is undefined? should there be a seperate f(x) function used? These are all the requirements, I'm not asking for anyone to do it for me since I have most of it done, but the ones with asterisks are the ones im confused with.

1. Input endpoints of interval of integration [a,b].

*2. Input the Integrand function f(x)

*3. Offer the user a menu of options for the sample point chosen in each subinterval (left, right endpoints, midpoint and random point within subinterval)

4. Plot function on [a,b]

5. For regular partition of [a,b], plot approx. rectangles under graph f(x)

6. Compute Sum under rectangles

7. Display Riemann sum on the figure

8. Output a well-formatted table of rectangle areas for n = 2, 4, 8, 16, 32, 64, 128, 256.

9. Record frames for the cases n = 2, 4, 8, 16, 32, 64, 128, 256, and display movie showing convergence of rectangles.

function riemann_krr(a,b,n)

zz = linspace(a,b);

yy = f(zz); yy1 = g(zz);

w = 0*zz;

plot(zz,yy,zz,yy1,zz,w,'k');

for j = 1:20
    n=2*j; 
    x=linspace(a,b,n+1);
    xr = x+rand(1,n+1)*(b-a)/n;
    hold on

for i = 1:n

      ys = f(xr(i)); yl = g(xr(i));
      xp = [x(i) x(i) x(i+1) x(i+1)];
      yp = [yl ys ys yl];
      fill(xp,yp,'b')
      plot(xp, yp)
      whitebg([.478, .617, .9])
      set(gcf,'Color',[.549 .09 .09]);figure(1)
  end
  plot(zz,yy,zz,w,'k')
  M(j) = getframe;
  pause(.5)
  clf
  hold off
  end
  movie(M)

Answer 1

[Geoff Hayes]

Keith - you have only mentioned part of the error message, that something is undefined. Presumably it is f and g since your third line of code is

 yy = f(zz); yy1 = g(zz);

and f and g are not defined prior to their use here. If you want f to be any function (so long as it accepts a scalar input and returns a scalar output) then it must be defined as an input variable in your function signature like

 function riemann_krr(f,a,b,n)

f is a handle to a function. See function handles for details on how to create a function handle. (Something similar will have to be done for g as well.)

As for the third point (from above) it seems that you are required to build a GUI that will allow the user to choose which (left, right, middle) Riemann sum he or she wishes to compute.