Why doesn't my code recognize my function outputs

Whenever I try to run my code I get an error saying that survivalProb does not exist but its an output

Im trying to create a loop that codes serveral different lines but I'm only gettig one line

clear
close all
clc
% Initialize data for component 
d=.005; % diameter in m 
A=(pi/4)*d^2; % bolt cross-sectional area 
IdealS=750000; % ideal strength in Pa   

% Set load schedule 
F= [10:.1:20]; % forces 
%limits of each stresses
S=F./A;

% stresses   

% Sample strength variability 
var = [.01 .12 .04 .08]; % percent variability in strength for each batch 
nSamp = [100 150 125 95]; % number of samples in each batch


for J=1:4
testStats(IdealS, var(J), nSamp(J), S);
plot(F,survivalProb,'LineWidth',4)
end
grid on
xlabel('Force Applied')
ylabel('Survival Probability')
function [survivalProb, avgSurvival] = testStats(IdealS,var,nSamp,S)
S2=S-S*var;
S1=S+S*var;
S=(S1-S2)*rand+ S2;
survivalProb= S<=IdealS; 
survivalProb=double(survivalProb)
avgSurvival=sum(survivalProb,'all')/nSamp
end

Answer 1

[Star Strider]

Yopu code does not specifically ask for that variable.

Try this instead:

for J=1:4
    [survivalProb, avgSurvival] = testStats(IdealS, var(J), nSamp(J), S);
    plot(F,survivalProb,'LineWidth',4)
end

That returns both outputs.