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Comparing ray/src/cal/cal/norm.cal (file contents):
Revision 1.3 by greg, Wed Apr 19 22:09:12 2017 UTC vs.
Revision 1.4 by greg, Sun Sep 12 17:04:41 2021 UTC

# Line 15 | Line 15 | NORMF : 1/sqrt(2*PI) ;
15  
16   Z(u) : NORMF * exp(-u*u/2) ;
17  
18 + { ### Old approximation:
19 +
20   Q2(t) : t*(.31938153+t*(-.356563782+t*(1.781477937+
21                  t*(-1.821255978+t*1.330274429)))) ;
22  
23   Q1(u) : Z(u) * Q2(1/(1+.2316419*u)) ;
24  
25   Q(u) : if( u, Q1(u), 1-Q1(-u) ) ;
26 +
27 + ### erf() gives us exact value: }
28 +
29 + Q(u) : .5 - .5*erf(u/sqrt(2)) ;
30  
31   u2(t) : t - (2.515517+t*(.802853+t*.010328))/
32                  (1+t*(1.432788+t*(.189269+t*.001308))) ;

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