How to add noise to signal

Hello

I am a beginner in using MATLAB. And I am working on a project for indoor localization. I have 4 accesses points. the codes that I wrote will first generate synthetic data according to some parameters entered by the user of the program. then some calculation is done to find the location of this points and thier distances from tha access points. then in one part of this project I should add noise to the received signals. I used the following code to add the noise

            PrAP1 = ((-10*app.n*log10(app.AP1_dist))+app.AP1_A); %to calculate the power of signal
            PrAP2 = ((-10*app.n*log10(app.AP2_dist))+app.AP2_A);
            PrAP3 = ((-10*app.n*log10(app.AP3_dist))+app.AP3_A);
            PrAP4 = ((-10*app.n*log10(app.AP4_dist))+app.AP4_A);
            
            Si= size(PrAP1,1);  %to know the size of the power vector
            rand1= rand(Si,1);  %generate random numbers to use as probability in norminv function
            rand2= rand(Si,1);
            rand3= rand(Si,1);
            rand4= rand(Si,1);
            
            
            PrAP1= PrAP1 + (norminv(rand1,0,app.noise)); %add the noise to the calculated power 
            PrAP2= PrAP2 + (norminv(rand2,0,app.noise));
            PrAP3= PrAP3 + (norminv(rand3,0,app.noise));
            PrAP4= PrAP4 + (norminv(rand4,0,app.noise));

After calculating the power matrix there is other codes to generate estimated points according to these values and at the end it calculates the average error between the synthetic data and the estimated data.

the code worked and give me good results. For example when I put the noise as 0.0001 it gives me average error of 0

but my problem is when I put the noise = 0 it returns NAN. what causes this problem? And how can I solve it?

I hope that my question is clear

[KALYAN ACHARJYA]

Can you illustrate the problem in simpler (more general) way?

norminv(0.0001)
ans =
   -3.7190
>> norminv(0)
ans =
  -Inf

[LB]

norminv function is as follows : norminve(p,mu,sigma)

it will always give inf if sigma =0 ???