Index: /trunk/Mars/mbase/MMath.cc
===================================================================
--- /trunk/Mars/mbase/MMath.cc	(revision 11425)
+++ /trunk/Mars/mbase/MMath.cc	(revision 11426)
@@ -223,4 +223,14 @@
 }
 
+// --------------------------------------------------------------------------
+//
+// Returns: 1 - exp((x/sigma)^2 / 2)
+//
+Double_t MMath::GaussProb2D(Double_t x, Double_t sigma)
+{
+    const Double_t xs = x/sigma;
+    return 1 - TMath::Exp(-xs*xs/2);
+}
+
 // ------------------------------------------------------------------------
 //
@@ -720,5 +730,5 @@
 //     Q := (3*b - a^2)/9
 //     R := (9*b*a - 27*c - 2*a^3)/54
-//     D := Q^3 + R^2                          % polynomial discriminant
+//     D := R^2 -Q^3                           % polynomial discriminant
 // 
 //     if (D >= 0) then                        % complex or duplicate roots
Index: /trunk/Mars/mbase/MMath.h
===================================================================
--- /trunk/Mars/mbase/MMath.h	(revision 11425)
+++ /trunk/Mars/mbase/MMath.h	(revision 11426)
@@ -17,4 +17,5 @@
 {
     Double_t GaussProb(Double_t x, Double_t sigma=1, Double_t mean=0);
+    Double_t GaussProb2D(Double_t x, Double_t sigma=1);
 
     template <class Size, class Element> void ReSortImp(Size n, Element *a, Bool_t down=kFALSE);