Trying to Create a Riemann Sum function from scratch, keep getting function error.

So i have to create a riemannsum calculator function, its been a little bit since ive used MatLab, but this seems right i just dont understand why i keep getting this error.

function [ Result ] = RiemannSum(Fun,a,b) %This function will calculate the riemann sum of a function defined from an %interval from a to b. This will be done using 10 subintervals.

dx=(b-a)/10;

XS=(a+(dx/2):dx:b-(dx/2));

Result=sum((feval(Fun,XS)).*dx);

The error i get is : RiemannSum(2*x,1,10) Undefined function or variable 'x'.

Even if i set x=XS it doesnt fix the error, im really stuck here.

Or when i tinker around and first run x=[] ill get this error instead.

Error using feval Argument must contain a string or function_handle.

Error in RiemannSum (line 6) Result=sum((feval(Fun,XS))*dx); end

Answer 1

[Rick Rosson]

Please type the following at the MATLAB Command Prompt:

   F = @(x) 2*x;
   R = RiemannSum(F,1,10);

[Amar]

That's fine and dandy but for this assignment I need the function to take the function I want evaluated as an input. Or is there no way to do this without defining it beforehand. What i need is for me to type RiemannSum(x^2,1,10) and it'll calculate the riemann sum for x^2 from 1 to 10. I know what it needs to do mathematically but MatLab isn't cooperating with my brain haha.

[Rick Rosson]

That is exactly what this solution does. It takes any function as an input argument.

Please try:

G = @(x) 3*x^2;
R = RiemannSum(G,1,10);

H = @(x) cos(x);
R = RiemannSum(H,1,10);

That is the whole point of using an anonymous function.

[Amar]

Okay, now is there any way instead of storing the function in H or G or declaring it beforehand, it THE FUNCTION ITSELF would be the input argument?

[Rick Rosson]

I don't know if this will work, but you could try:

   R = RiemannSum(@(x) 2*x, 1, 10)

I am not sure why it matters. What difference does it make?

[Amar]

Blame my professor, he's a picky man.

[Rick Rosson]

Did it work?

[Amar]

Yes it did finally, thank you very very much. I know it must have been a bit annoying.

Answer 2

[Amar]

I was told by an individual to just put my function in '' and that did not work, i now get this error: Invalid function name '2*x'.

Error in RiemannSum (line 6) Result=sum((feval(Fun,XS)).*dx);

[Rick Rosson]

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