Can someone help vectorize this loop?
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Hi, Can this code be vectorized. If so, can someone help me to do so. Thanks in advance. C is a 201*201 2D matrix.
for l=2:N-1
for m= 2:N-1
rd=randi([0 8]);
if rd ==0
C(l,m)=C(l,m) - 1;
C(l,m+1)=C(l,m+1)+1;
elseif rd ==1
C(l,m)=C(l,m) - 1;
C(l+1,m+1)=C(l+1,m+1)+1;
elseif rd ==2
C(l,m)=C(l,m) - 1;
C(l+1,m)=C(l+1,m)+1;
elseif rd ==3
C(l,m)=C(l,m) - 1;
C(l+1,m-1)=C(l+1,m-1)+1;
elseif rd ==4
C(l,m)=C(l,m) - 1;
C(l,m-1)=C(l,m-1)+1;
elseif rd ==5
C(l,m)=C(l,m) - 1;
C(l-1,m-1)=C(l-1,m-1)+1;
elseif rd ==6
C(l,m)=C(l,m) - 1;
C(l-1,m)=C(l-1,m)+1;
elseif rd ==7
C(l,m)=C(l,m) - 1;
C(l-1,m+1)=C(l-1,m+1)+1;
elseif rd ==8
C(l,m)=C(l,m);
end
end
end
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Answers (1)
Matt J
on 28 Jul 2015
reorder=[8 9 6 3 2 1 4 7 5];
[X,Y]=ndgrid(1:3);
Increm = sub2ind(size(C),X,Y)-sub2ind(size(C),2,2);
Increm(5)=0;
Increm=Increm(reorder);
Lookup=randi([1,9],size(C)-2);
Lidx=reshape(1:numel(C),size(C));
Lidx([1,end],:)=[];
Lidx(:,[1,end])=[];
Linc= Increm(Lookup);
LidxInc=Lidx+Linc;
subs=[Lidx(:),LidxInc(:)];
v=logical(Linc(:));
val=[-v,v];
Delta=accumarray(subs(:),val(:),[numel(C),1]);
C=C+reshape(Delta,size(C));
1 Comment
Matt J
on 28 Jul 2015
Edited: Matt J
on 28 Jul 2015
For comparison, you can verify that the above produces the same result as this slightly rewritten, but equivalent version of your code:
N=length(C);
Rd=Lookup.'-1; %<-----modified
cc=0;
for l=2:N-1
for m= 2:N-1
cc=cc+1;
rd=Rd(cc); %<-----modified
if rd ==0
C(l,m)=C(l,m) - 1;
C(l,m+1)=C(l,m+1)+1;
elseif rd ==1
C(l,m)=C(l,m) - 1;
C(l+1,m+1)=C(l+1,m+1)+1;
elseif rd ==2
C(l,m)=C(l,m) - 1;
C(l+1,m)=C(l+1,m)+1;
elseif rd ==3
C(l,m)=C(l,m) - 1;
C(l+1,m-1)=C(l+1,m-1)+1;
elseif rd ==4
C(l,m)=C(l,m) - 1;
C(l,m-1)=C(l,m-1)+1;
elseif rd ==5
C(l,m)=C(l,m) - 1;
C(l-1,m-1)=C(l-1,m-1)+1;
elseif rd ==6
C(l,m)=C(l,m) - 1;
C(l-1,m)=C(l-1,m)+1;
elseif rd ==7
C(l,m)=C(l,m) - 1;
C(l-1,m+1)=C(l-1,m+1)+1;
elseif rd ==8
C(l,m)=C(l,m);
end
end
end
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