Probability density function (pdf) of a folded-normal random variable with ${\displaystyle \mu =1}$, ${\displaystyle \sigma =1}$. The graph is generated using gnuplot:

set terminal svg enhanced size 640 360 set samples 1001  # high quality set border 31 linewidth .3 # thin border set output "folded_normal.svg"  set notitle set xrange [-3:5] set ytics 0.1  sigma=1.0 mu=1.0 n(x)=1.0/(sqrt(2.0*pi)*sigma) * exp( -(mu-x)**2/(2.0*sigma**2) ) nreflect(x)= (x<0) ? 1/0 : n(-x) fn(x)= (x<-0.01) ? 0 : (x<0) ? 1/0 : (n(x) + n(-x))   set arrow 1 from  0,0 to  0,0.5 nohead lt 0  plot	n(x) title "normal density",\ 	fn(x) title "folded-normal density" lw 3,\ 	nreflect(x) notitle with l lt 0 

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