Finding indices in matrix with find() function

Hi all,

I'm having some difficulty using the find() function with multiple conditions. Below is a sample of what I'm referring to. LUTi and LUTj are matrices with defined values.

>> LUTi(60,240)

ans =

     0
>> LUTj(60,240)

ans =

    1.0000

>> [theta1 theta2] = find(LUTi == 0 & LUTj == 1)

theta1 =

   Empty matrix: 0-by-1

theta2 =

   Empty matrix: 0-by-1

The output I'm expecting to see is [60,240], but instead, it's returning an empty matrix. Am I inputting the 2 conditions incorrectly? Thank you in advance.

Alexis

Answer 1

[Paulo Silva]

You are using the find function in two matrices at the same time, that's not a good idea

[row column]=find(LUTi==0)

[row1 column1]=find(LUTj==1)

[Jos (10584)]

Why not?

I assume that both matrices have the same size (otherwise an error would have been trhown by AND) and Alexis is looking for the indices where both comparisons are true.

Answer 2

[Matt Tearle]

I think you may have fallen for an old trap. Please enter

1 - LUTj(60,240)

and see what the result is. I'm going to take a guess that it's not 0. Given the way it says LUTj(60,240) is "1.0000", I'm guessing that the value is not exactly 1, but 1 + some roundoff. In that case, testing ==1 will return false. The solution is to test something like

abs(x - 1) < tol

where tol is some small value.