how to read and change entries in a large array

I have a 842x650, i want to read through every entry, check its value and if its under a certain value change it to zero. Any help would be amazing !!

Answer 1

[KL]

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

[KL]

I'd also recommend reading a bit about floating point numbers. Various threads with extensive explanations exist, probably start with this one: https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero