how i can fix noise estimated value everytime if i reopened matlab.

I have implemented noise estimation algorithm in matlab,and i have added noise using 'randn' function.now i run this program in matlab and i take value of noise estimated.

now i close the matlab. and reopened it. and open the above program and i view the value of noise estimated, it is little different from previos value. i khow why this done. because randn function adds the different value at every pixel generally everytime and total deviation of noise matrix makes is equal to standard deviation that i have defined in ''sd*randn''.

so how i can fix noise estimated value everytime if i reopened matlab.