How do I make the element zero, if its adjacent column element is zero?

Hello,

Assume, I have the following 9x2 matrix. When there is a zero in the second column, I want to make the first column's same row element zero too.

12  0
11  0
10  6
12  0
11  3
10  0
12  0
11  5
10  0

This will become like:

0  0
0  0
10  6
0  0
11  3
0  0
0  0
11  5
0  0

Thank you so much

Answer 1

[per isakson]

Try

>> is_zero = A(:,2)==0;
>> A(is_zero,1)=0;
>> A
A =
     0     0
     0     0
    10     6
     0     0
    11     3
     0     0
     0     0
    11     5
     0     0

and see Using Logicals in Array Indexing

[Taner Cokyasar]

Thank you so much for both of your comments. I was thinking that using 'if' were the only way of doing it.

Answer 2

[Star Strider]

That can actually be done in one line of code:

M = [12  0
    11  0
    10  6
    12  0
    11  3
    10  0
    12  0
    11  5
    10  0];

M(M(:,2) == 0,1) = 0

M =
     0     0
     0     0
    10     6
     0     0
    11     3
     0     0
     0     0
    11     5
     0     0

[per isakson]

Yes, but I think two lines make a more comprehensible code.

[Taner Cokyasar]

Can you help me also on this:

I have the following sample vector named Zvalues:

 Variable Name(Zim)    Zvalues
 Z11                      0
 Z12                      0
 Z13                      1
 Z21                      0
 Z22                      1
 Z23                      0
 Z31                      0
 Z32                      1
 Z33                      0

I have created a zero 3x9 sized matrix as following:

 Y= zeros(3, 9);

I want to fill this matrix with an if condition, as the following example:

 if Zim=1, Yim=1

 Y13 = 1 because Z13 = 1
 Y22 = 1 because Z22 = 1
 Y32 = 1 because Z32 = 1

The following matrix is what I want to reach at the end. 'Y's represent variable names, they are not a part of the matrix .

Y11 Y12 Y13 Y21 Y22 Y23 Y31 Y32 Y33

0   0   1   0   0   0   0   0   0  
0   0   0   0   1   0   0   0   0  
0   0   0   0   0   0   0   1   0

In other words, I want to formulate an Aeq matrix for coefficients of Y(im) variables given in the following equality constraint (to use with intlinprog):

 Y(im)=t(m)-Z(im)*f(i)        %construct this constraint for variables if Z(im)=1    (Zim is same as Zvalues)
                %There is nothing to do with the RHS of the equality. It is just given to make the question more clear.

As seen in the equation, coefficients of all Y(im) variables are 1. In my sample I have 9 Y(im) variables, since i=3 and m=3. I will have larger dimensions. So, I need a MATLAB formulation for this mathematical form.

Thanks for help.

[per isakson]

Adding a question in a comment to an existing question with an accepted answer doesn't attract many viewers. I think it is better to open a new question.

I have problems understanding your "pseudo indexing".

"Y13 = 1 because Z13 = 1" &nbsp Here is a piece of elegant Matlab code. (Not sure it is relevant, though.)

>> A = zeros(3,4,2);
>> B = randi( [1,2], size(A) );
>> A(B==1)=1;  % or A(B==1)=B(B==1);
>> B
B(:,:,1) =
     2     2     1     2
     1     1     1     2
     2     2     2     1
B(:,:,2) =
     2     1     1     2
     1     1     2     1
     1     2     1     2
>> A
A(:,:,1) =
     0     0     1     0
     1     1     1     0
     0     0     0     1
A(:,:,2) =
     0     1     1     0
     1     1     0     1
     1     0     1     0
>>