It's easier to answer with an example. Let's say we have a matrix of 5x5 with random numbers and you want to find the elements that are between 0.5 and 0.75 and then make it to zero.
A = rand(5,5)
ind = A>=0.5 & A<=0.75;
A(ind) = 0;
A
and now an example result is (before and after),
A =
0.8001 0.1455 0.1450 0.4018 0.2400
0.4314 0.1361 0.8530 0.0760 0.4173
0.9106 0.8693 0.6221 0.2399 0.0497
0.1818 0.5797 0.3510 0.1233 0.9027
0.2638 0.5499 0.5132 0.1839 0.9448
A =
0.8001 0.1455 0.1450 0.4018 0.2400
0.4314 0.1361 0.8530 0.0760 0.4173
0.9106 0.8693 0 0.2399 0.0497
0.1818 0 0.3510 0.1233 0.9027
0.2638 0 0 0.1839 0.9448
