Building a function to display of the sum of matrices at different powers in Matlab

Question

I'm trying to write a for loop for the sum A+A^2+A^3+..+A^n.

Here is my code:

function [ x ] = Untitled2( A , n )

for k=1:n,

x =sum(A^k)

end

The problem I'm having with this is this function is listing the matrix A to each power without adding them. What can I do to add these together? Thank you in advance

score 2 · Accepted Answer · answered Nov 04 '13 at 22:16

2

Matlab's sum returns the sum along the first dimension not equal to one. If you want to add to x you would be best to use:

function[x]=Untitled(A,n)

x=zeros(size(A));

for k=1:n

x = x + A^k

end

answered Nov 04 '13 at 22:16

Jeremy Upsal

1,443

This worked like a charm? An additional question: how would this work differently for a while loop? – Heath Huffman Nov 04 '13 at 22:18
1

It depends on what your while conditional is, I assume you want to iterate the same way until your have reached n sums:
while k<n+1 x=x+A^k end
– Jeremy Upsal Nov 04 '13 at 22:19
1

@Heath Huffman If this answer sufficiently answered your question, consider accepting it by clicking the check mark on the side, and up-voting the question. Your answerers will appreciate it! – dinkelk Nov 04 '13 at 22:42
With that code on the while loop, I am receiving the following error: undefined function for variable 'k'. How can I fix this? – Heath Huffman Nov 04 '13 at 22:46
1

First define k=0. – Jeremy Upsal Nov 04 '13 at 22:47
I got a recursive error. How can I limit k? – Heath Huffman Nov 04 '13 at 22:50
1

k should stop iterating when k=n+1, what are you inputting for n? I do not mind helping, but @dinkelk 's suggestion is true and appreciated. – Jeremy Upsal Nov 04 '13 at 22:52
Done and done! I ran the function for a 2x2 matrix and I let n = 4. I'm not sure why it happened. – Heath Huffman Nov 04 '13 at 22:54
And here is the code for reference: function [ x ] = Untitled3( A, n ) x=zeros(size(A)); k = 0; while k<(n+1), x = x+A^k
end
– Heath Huffman Nov 04 '13 at 23:04
I'm sorry, I forgot to explicitly tell you to increment k in the while loop. After x=x+A^k, add a line that has k=k+1;. – Jeremy Upsal Nov 05 '13 at 01:16

Building a function to display of the sum of matrices at different powers in Matlab

1 Answers1