How to replace elements in a matrix using logical

Hello,

I would like to set some columns to zero for certain rows indicated by a logical. For instance, if we have a matrix X

X =

1 1 1 1

2 2 2 2

3 3 3 3

4 4 4 4

Suppose I have a logical that is true for row 3 and 4. Then I would like to replace column 3 to 4 with zero for row 3 and 4, so that the result is:

X =

1 1 1 1

2 2 2 2

3 3 0 0

4 4 0 0

To indicate the columns I want to replace I have tried things like 3:end, or size(B,1):end, but I get a message Subscript indices must either be real positive integers or logicals.

However, even if I only use integers, let's say 3:4, I still get the same message. What am I doing wrong? Thanks for your advice!

Answer 1

[Ameer Hamza]

Try this

X = [
     1     1     1     1
     2     2     2     2
     3     3     3     3
     4     4     4     4];
tf = [false; false; true; true];

X(tf, tf) = 0;

Result

>> X
X =
     1     1     1     1
     2     2     2     2
     3     3     0     0
     4     4     0     0

[Ara Jo]

Thanks for the answer! I have tried with two logicals, one for rows and another for columns, and I still get the same message..

[Ameer Hamza]

Can you paste your code which gives error?