# how to create this matrix?

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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

Brian Hart on 22 Dec 2018
Edited: Brian Hart on 22 Dec 2018
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

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 on 22 Dec 2018
Yep, missed a set of parenthesis. Corrected, thanks.

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)

#### 1 Comment

Stephan on 22 Dec 2018
+1

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