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Find an element of a matrix equal to a constant

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cyberdyne
cyberdyne 2011-3-29
Hi,
If B is a matrix i need to find the index of element that is equal to a constant c where the constant c is undoubtedly somewhere in the matrix.
I tried to do:
B(:,B(2,:)==c)
but there are some problems with logical operator ==
It returns me "Empty matrix"

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回答（1 个）

Matt Fig
Matt Fig 2011-3-29
If you are looking for the linear index:
I = find(B==c);
If you are looking for the subscript index:
[I,J] = find(B==c);
I hope you are not experiencing a floating point issue???
Whenever I hear somebody say they cannot find a value that they just know is in an array, I wonder if they are not about to learn the joys of floating point arithmetic.
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Walter Roberson
Walter Roberson 2011-3-29
Yup, see the link Matt posted about floating point issues.

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