alpha = 0.05 ;
n = 0:250 ;
rc = cor_crit(n, alpha) ;
plot(n, rc) ;
grid on ;
xlabel('sample size') ;
ylabel('critical correlation') ;
legend({'1-tailed' '2-tailed'}, 'box', 'off', 'location', 'northeast') ;
text(110, 0.9, '{\alpha = 0.05}') ;
print -dsvg cor_crit.svg

%% usage: rc = cor_crit (n, alpha)
%%
%% critical correlation values from sample size
function rc = cor_crit (n, alpha)

   df = n - 2 ;
   tc(1,:) = tinv(1-alpha, df) ;
   tc(2,:) = tinv(1-alpha/2, df) ;

   rc = tc ./ sqrt(df + tc.^2) ;

end