how to create this matrix?

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diadalina
diadalina am 22 Dez. 2018
Kommentiert: Stephan am 22 Dez. 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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Brian Hart
Brian Hart am 22 Dez. 2018
Bearbeitet: Brian Hart am 22 Dez. 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 Kommentare
Guillaume
Guillaume am 22 Dez. 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 am 22 Dez. 2018
Yep, missed a set of parenthesis. Corrected, thanks.

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Weitere Antworten (2)

Guillaume
Guillaume am 22 Dez. 2018
Bearbeitet: Guillaume am 22 Dez. 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 am 22 Dez. 2018
Bearbeitet: Stephan am 22 Dez. 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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