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Show column which starts with certain numbers

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Jakub
Jakub 2013-4-12
Hi, i have matrix size 500x500. And i need to find column which starts with vector [1 2]'. Only one column in whole matrix starts with these two certains numbers. The matrix looks something like this
[1 1 1 1 1]
[1 2 3 4 5]
[1 2 3 4 5]
I need function that tells me column number two starts with 1 and second value is 2.
Thanks for help!

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Cedric
Cedric 2013-4-12
If your matrix is named M, you can do
col = M(1,:) == 1 & M(2,:) == 2 ;
to get a vector of logicals indicating the relevant column, and
find(col)
to get the column number.

更多回答（1 个）

Youssef Khmou
Youssef Khmou 2013-4-12
编辑：Youssef Khmou 2013-4-12
hi, try :
a=rand(500);
a(1:2,312)=[1 2]; % for example the column 312 starts with [1 2]
b=a(1:2,:);
test=[1 2]';
for n=1:length(b)
diff(n)=norm(b(:,n)-test);
end
Index=find(diff==0);
Index is the number of the column,

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