I don't understand this command : F=find(B>4)

If I have this matrix :

B=[1 2 3 4; 5 6 7 8], why when I run this -> F=find(B>4) , the result is:

2

4

6

8

?

Thank you

Answer 1

[Cris LaPierre]

That looks correct. What is it you are expecting?

Since the output is returning a single index for each value found, it is uslng linear indexing. You can read more about that here: https://www.mathworks.com/help/matlab/math/array-indexing.html#MatrixIndexingExample-2

If you prefer row & column index, use the following syntax

[row,col] = find(___)

You can read more about the find function here: https://www.mathworks.com/help/matlab/ref/find.html

[Roberta]

Thank you (:

Answer 2

[Paul]

B is a 2D matrix.

B=[1 2 3 4; 5 6 7 8]

B = 2×4

1 2 3 4 5 6 7 8

This command finds the "linear indices" of the elements of B that satisfy the criteria

find(B>4)

ans = 4×1

2 4 6 8

The linear indices are the indices of B when it's viewed a s 1D vector formed by vertically concatenating its columns, which can be shown as

B(:)

ans = 8×1

1 5 2 6 3 7 4 8

The 2nd, 4th, 6th, and 8th elements of B(:) are the elements greater than 4

[Roberta]

Thank you :-))