How to ignore negative indices or assign it to zero in a loop

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MD JAHIDUL HAQUE KHAN 2021-5-5

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评论： MD JAHIDUL HAQUE KHAN 2021-5-5

x=[1 2 -1 -3 -4]
h=[0 1 3]
n=length(x)
m=length(h)
y=zeros(n,m)
for i=1:n
  for  j=1:m
    
     if i-j>0 
          y(i,j)=h(j)*x(i-j+1)
     else
         y(i,j)=0 % My problem is here to assign if the element x(i-j) does not exist return zero
                  %but it is ignoring all the element in the matrix that is (i-j)< zero
     end
                    
  end
end

I have tried approach this problem by setting up a matrix, however i did not start loop from zero since it is same both way if i am right

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Answer 1

Stephan 2021-5-5

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https://ww2.mathworks.cn/matlabcentral/answers/822100-how-to-ignore-negative-indices-or-assign-it-to-zero-in-a-loop#answer_692510

编辑：Stephan 2021-5-5

在 MATLAB Online 中打开

It is not needed to make the elements zero - they are already, because you preallocated y with zeros:

x=[1 2 -1 -3 -4]
h=[0 1 3]
n=length(x)
m=length(h)
y=zeros(n,m)
for i=1:n
  for  j=1:m
    
     if i-j>0 
          y(i,j)=h(j)*x(i-j+1)
     end
                    
  end
end

gives:

% alot of stuff
% ...
y =
     0     0     0
     0     0     0
     0     2     0
     0    -1     6
     0    -3    -3

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Stephan 2021-5-5

在 MATLAB Online 中打开

use:

if i-j>=0

instead of

if i-j>0

MD JAHIDUL HAQUE KHAN 2021-5-5

Thanks Stefan

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How to ignore negative indices or assign it to zero in a loop

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