These are the outputs of the min() function. b is the location of the minimum value. ~ means that the first output argument, the minimum value itself, is not to be assigned to any variable.
If the input is a vector, then you can do the following:
[val,idx] = max(b);
whereval will be the maximum value of 12 andidx will be the index of 4. Typehelp max for more details. (It gets a little more complicated when the input is matrix.)
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