# matrix multiplication with probability

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Santhosh Chandrasekar on 11 Feb 2018
Hi, I want to assign a probability of multiplication for each value in a 3X3 matrix and multiply it by a random number. Can anyone please help me with this.
##### 2 CommentsShowHide 1 older comment
Santhosh Chandrasekar on 11 Feb 2018
Edited: Santhosh Chandrasekar on 12 Feb 2018
Thank you Jan for your answer, I sincerely appreciate it. but my requirement is for example
A = [1 0.5 1; 0.6 0.3 0.4; 0.4 0.5 1];
K= 1:1:10
a = rand;
C= [a 0 0]; here i want to assign probabilities to the 3 positions of 'C' where 'a' can be assigned i.e C = [10% 20% 30%] so during every iteration, a random 'a' is generated and it is placed in one of the position of 'C' based on the assigned probability and 'C' will get multiplied with 'A'

Roger Stafford on 12 Feb 2018
Edited: Roger Stafford on 12 Feb 2018
If p is a matrix the same size as A with the probability values you describe, do this:
SA = size(A);
a = rand(SA);
A = A + (A.*a-A).*(rand(SA)<=p);
At each element of A it is multiplied by the random number in ’a’ with probability in the corresponding element in p. Otherwise the element is unchanged.
It is possible you meant 'a' to be a single random scalar value rather than a matrix of them. If so, change the code to:
a = rand;
A = A + ((a-1)*A).*(rand(size(A))<=p);
Santhosh Chandrasekar on 14 Feb 2018
I got it. thank you very much!.

### More Answers (1)

Jan on 11 Feb 2018
Maybe:
A = [1 0.5 1; 0.6 0.3 0.4; 0.4 0.5 1];
for k = 1:10
a = rand;
B = A * a;
...
end
##### 1 CommentShowHide None
Santhosh Chandrasekar on 12 Feb 2018
Edited: Santhosh Chandrasekar on 12 Feb 2018
Thank you Jan for your answer, I sincerely appreciate it. but my requirement is for example
A = [1 0.5 1; 0.6 0.3 0.4; 0.4 0.5 1];
K= 1:1:10
a = rand;
C= [a 0 0]; here i want to assign probabilities to the 3 positions of 'C' where 'a' can be assigned i.e C = [10% 20% 30%] so during every iteration, a random 'a' is generated and it is placed in one of the position of 'C' based on the assigned probability and 'C' will get multiplied with 'A'

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