How to use find function to get log of the values?

Hi,

I'm trying to create a new array B where the values are logs of array A (if greater than 1). If the value is smaller or equal to 1 I need to add 39 to these. So far I'm up to here but I don't know how to add that 39

A=[8 14 3;-13 1 42;-39 -8 15];
B=zeros(size(A));
l=find(A>1);
B(1:length(l))=log(A(l));

Thanks in advance

Answer 1

[Akiva Gordon]

Use logical indexing to accomplish this:

A = [8 14 3; -13 1 42; -39 -8 15];

B = zeros(size(A));

Valid indices are those in which A is greater than 1,

vi = logical(A>1);

Where we found a logical "true", take the log of that location in A,

B( vi) = log(A(vi));

For the other indices, add 39 to them,

B(~vi) = A(~vi)+39;

Is this the output you were expecting?

B =

      2.0794    2.6391    1.0986
     26.0000   40.0000    3.7377
           0   31.0000    2.7081

[Patrick]

Works! Thank you very much. I still have a lot to learn.

[Akiva Gordon]

No problem, Patrick!