MATLAB: Basic use of sum command help

commandhomeworkseriessum

Recall that a geometric sum is a sum of the form a + ar + ar2 + ar3 + . . ..
(a) Write a function file that accepts the values of r, a and n as arguments and uses a for loop to return the sum of the first n terms of the geometric series. Test your function for a = 3, r = 1/2 and n = 10.
S = 0;
a=3;
r=1/2;
for n=0:1:10;
  S=S+a*r^n;
end
S
This works, So I'm good here.
(b) Write a function file that accepts the values of r, a and n as arguments and uses the built in command sum to find the sum of the first n terms of the geometric series. Test your function for a = 3, r = 1/2 and n = 10. Hint: Start by defining the vector e=0:n-1 and then evaluate the vector R = r.^e. It should be easy to figure out how to find the sum from there
This is where I am stuck. Keep in mind that I have only been using MATLAB for about a week now. Any help is appreciated, I don't even know where I should start with this. Thank you.

Best Answer

Declare the function
function theSum = yourFunctionName(r, a, n)
In the function get rid of the "for" loop - just have n=0:1:10;
Then use .^ instead of ^. Then a few more little things you can get rid of - hopefully you can figure those out.
That should be more than enough hints for you to complete it.
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