Do not share screenshot but use the CODE environment
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If b is a vector, b > 0 is a vector of logical values. If you need to check if only one of the entry of b is larger than 0, use
if any(b>0)
Another thing is not proper in your code: the matrix A does not depend on m and it is constant through the iterations: you can move it outside the loop along with the statement w = 1;