Considering that -1 can be written as -1+(0/4), a pattern becomes clear:
1 -> -1+(0/4)
2 -> -1+(2/4)
3 -> -1+(4/4)
4 -> -1+(6/4)
5 -> -1+(8/4)
In general, say:
x -> -1+(y/4)
The pattern is that each time x is incremented by 1 on the left-hand side: x = (1, 2, 3, 4, 5), that corresponds to y being incremented by 2 on the right-hand side: y = (0, 2, 4, 6, 8). And y is 0 when x is 1.
Thus we can say that y = 2*(x-1), so that the rule is:
x -> -1+(2*(x-1)/4)
or, simplifying:
x -> -1+(x-1)/2
So if x is your m-by-n matrix, then the transformed version of x is -1+(x-1)/2.
m = 3;
n = 4;
x = randi(5,[m,n])
new_x = -1+(x-1)/2
