how to create this matrix?

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diadalina
diadalina 2018-12-22
评论： Stephan 2018-12-22
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 2018-12-22
编辑：Brian Hart 2018-12-22
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 个评论
Guillaume
Guillaume 2018-12-22
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 2018-12-22
Yep, missed a set of parenthesis. Corrected, thanks.

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更多回答（2 个）

Guillaume
Guillaume 2018-12-22
编辑：Guillaume 2018-12-22
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 2018-12-22
编辑：Stephan 2018-12-22
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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