Can Any one help with this plz

*lnP(m+1)- lnP(m) < allowable change* 
% where lnP(m+1) , lnP(m) , allowable change is given
% its should do this
* lnP(m+1) = lnP(m) +/- allowable change* 
% +/- is causing my head-in , How can I write this in Matlab

Answer 1

[Walter Roberson]

lnP(m+1) = lnp(m) + (rand() * 2 - 1) * allowable_change;

[Nasir Qazi]

for +/- means in case of '+' the give me top value and in case of '-' this will give me lower value ' not the random value' so lnP(m+1) has 2 values one is top value and one is lower that's what I want .