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how to create this matrix?

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diadalina
diadalina on 22 Dec 2018
Commented: Stephan on 22 Dec 2018
can anyone help me to construct this matrix
blj=(-2)^j-l if l<j
blj=1 if l=j
blj=0 if l>j

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Accepted Answer

Brian Hart
Brian Hart on 22 Dec 2018
Edited: Brian Hart on 22 Dec 2018
Hi diadalina,
I think it would look something like this...
iLength = 5; %rows
jLength = 7; %cols
b=zeros(iLength, jLength);
for i = 1:iLength
for j = 1:jLength
if i == j; b(i,j) = 1; end
if i < j; b(i,j) = (-2)^(j-i); end
end
end
disp(b)
gives a result of:
1 -2 4 -8 16 -32 64
0 1 -2 4 -8 16 -32
0 0 1 -2 4 -8 16
0 0 0 1 -2 4 -8
0 0 0 0 1 -2 4

  2 Comments

Guillaume
Guillaume on 22 Dec 2018
It is unclear if the formula in the question is as written or which would make more sense. One thing for sure, it's not likely to be which is what you calculate.
Brian Hart
Brian Hart on 22 Dec 2018
Yep, missed a set of parenthesis. Corrected, thanks.

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More Answers (2)

Guillaume
Guillaume on 22 Dec 2018
Edited: Guillaume on 22 Dec 2018
Assume your formula is and not what you have written:
nrows = 5; %number of rows. You haven't specified
ncols = 7; %number of columns. You haven't specified
b = toeplitz([1, zeros(1, nrows-1)], (-2).^(0:ncols-1))
If the formula is what you have actually written, , then
b = triu((-2).^(1:ncols) - (1:nrows)', 1) + eye(nrows, ncols)

Stephan
Stephan on 22 Dec 2018
Edited: Stephan on 22 Dec 2018
Hi,
do you want a square matrix? Is the calculation correct without any brackets? My calculation follows the way you wrote the formula - if wrong set the brackets corresponding to your expected result.
Then try:
k=3;
[m,n]=meshgrid(1:k);
A=triu((-2).^n-m,1) + eye(k)
Best regards
Stephan

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