Matrix value change with conditions (x=y*(mask==1))

I have two matrix x,y and mask.

x = [1,1,1,1;...
     2,2,2,2;...
     3,3,3,3;...
     4,4,4,4];
y = [5,5,5,5;...
     5,5,2,5;...
     5,5,5,5;...
     5,5,5,5];
mask = [0,0,0,0;...
        1,1,1,1;...
        0,0,0,0;...
        1,1,1,1];

When try perform this:

x=y*(mask==1)

Result is:

x =
    10    10    10    10
    10    10    10    10
    10    10    10    10
    10    10    10    10

Why?

Answer 1

[madhan ravi]

(* performs matrix multiplication) perhaps you needed .* element wise multiplication

https://in.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

[pawel banasiak]

This is IF statement, not multiplication. Example:

x=2

y=5*(x==2)

Result:

x = 2

y = 5

Regards

[madhan ravi]

I am afraid you should take MATLAB onramp course to learn the basics of MATLAB. Also read the links I shared to understand what's going on.

https://blogs.mathworks.com/loren/2013/02/20/logical-indexing-multiple-conditions/

That is called logical indexing not if statement:

>> x=2

x =

     2

>> idx=x==2

idx =

  logical

   1

>> idx*5

ans =

     5

>> 

[pawel banasiak]

Thank you very much for the answer. My goal is to change the value in x into a value from y with condition mask without use FOR.

[madhan ravi]

Show how your expected result should look like with an example.

Perhaps you wanted to do:

x(mask==1)=y(mask==1)

[pawel banasiak]

many thanks!!! You helped me a lot