The calculation of 1/23 * [1 2 3] returns [0.041667 0.083333 0.125000].
I just want a display like [1/23 2/23 3/23]
You can specify format rat, to always display outputs as rational approximations (applies to both matlab and octave).
format rat
a = 1/23 * [1,2,3]
% a = 1/23 2/23 3/23
Or, you can use that "rat" or "rats" functions, to print (as strings) the rational approximations of a float array:
a = 1/23 * [1,2,3]
% a = 0.043478 0.086957 0.130435
rats(a)
% ans = 1/23 2/23 3/23
As Cris pointed out in the comments, this is simply a representational issue. The underlying floating-point representation of the result does not change. If you wish to work with fractions in a 'mathematical' sense, then you need to go about this a different way (possibly symbolic package, or dealing with numerators and denominators manually).