Matlab question, very stuck

Question

James Harrison 2021-1-10

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https://ww2.mathworks.cn/matlabcentral/answers/713503-matlab-question-very-stuck

评论： Image Analyst 2021-1-11

采纳的回答： Image Analyst

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I am very stuck with this question, any help would be appreciated.

function [New_Matrix] = sequence_matrix(n)
%UNTITLED4 Summary of this function goes here
%   Detailed explanation goes here
if n ==1
    v=2
elseif n==2
    v=3
elseif n>=3
    i(n) = 2*v(n-1) + 3*v(n-2)
i=zeros(n,n);
m = i;
i(1:n+1:end) = v
end

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Answer 1

Image Analyst 2021-1-10

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Close but not quite. Try it this way:

function [New_Matrix] = sequence_matrix(n)
%   Detailed explanation goes here
New_Matrix = zeros(n);
v = 2;
if n >= 2
	v = [2, 3];
end
if n >= 3
	for k = 3 : n
		v(k) = 2*v(k-1) + 3*v(k-2)
	end
end
for k = 1 : n
	New_Matrix(k, k) = v(k);
end
end

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James Harrison 2021-1-10

Yes this is almost perfect. I just have to make it say 'Error. Invalid input' if the value entered is less than 2

Image Analyst 2021-1-11

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At the beginning, after you assign New_Matrix, say

if n < 2
    warningMessage = sprintf('Error.  Invalid input.\nYou entered n = %d.\nn must be 2 or greater', n);
    uiwait(errordlg(warningMessage));
    return;
end

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Answer 2

William 2021-1-10

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Your program seems to be a little uncertain about whether v is a number or a vector, and it also doesn't assign the values correctly into the diagonal of the matrix i(). However, the general sequence of operations is correct. Let me suggest the following:

Create the vector v as a vector with n elements, using v = zeros(1,n);
Fill in the values of v(j), with v(1) = 2, v(2) = 3, and v(j) = 2*v(j-1) + 3*v(j-2) for all j > 2;
Then put the values of v into the diagonal of a matrix I using I = diag(v);

Let me know how it turns out!