Update documentation after introducing Conditinal and Inhibit.

Closes #28. Closes #29.

doc/fta_implementation.rst

@@ -15,6 +15,7 @@ Currently Supported Gate Types
 - NAND
 - XOR
 - NULL
+- INHIBIT
 
 Currently Supported Symbols
 ==============================
@@ -31,6 +32,7 @@ Currently Supported Event Types
 - Basic
 - House
 - Undeveloped
+- Conditional
 
 
 The Algorithm to Generate Minimal Cut Sets

doc/fta_probability_calc.rst

@@ -13,14 +13,15 @@ fault tree. However, note that this algorithm still assumes independence of
 primary events in the fault tree.
 
 
-Exact Probability Calculation Implementation
+The Exact Probability Calculation Implementation
 ========================================================
 
 The general probability formula for sets is expanded recursively.
 In each iteration, some sets are merged in order to account for common members
-in minimal cut sets. This algorithm is also used for series expansion.
+in minimal cut sets. This algorithm is also used for series expansion, giving
+the Sylvester-Poincaré expansion.
 
-Approximate Probability Calculation Implementation
+The Approximate Probability Calculation Implementation
 ========================================================
 
 Approximate calculations are implemented in order to reduce calculation
@@ -30,6 +31,25 @@ This feature is the default. The default value for series is set to N
 In general, it is impractical to include more than 8 sums, so the suggestion
 is to include between 4 and 8 sums.
 
+The Rare-Event Approximation
+=============================
+Given that probabilities of events are very small value less than 0.1, only the
+first series in the probability equation may be used as a conservative
+approximation; that is, the total probability is the sum of all probabilities
+of minimal cut sets. Ideally, this approximation gives good results for
+independent minimal cut sets with very low probabilities. However, if the cut
+set probabilities are high, the total probability may exceed 1.0.
+
+The Min-Cut-Upper Bound (MCUB) Approximation
+=============================================
+This method calculates the total probability by subtracting the probability
+of all minimal cut sets being successful from 1.0; thus, the total probability
+never exceeds 1.0. Non-independence of the minimal cut sets introduce
+the major discrepancy for this technique. However, the MCUB approximation
+provides non-conservative estimation for non-coherent trees containing
+*NOT* logic. There are other limitations described by Don Wakefield in
+"You Can't Just Build Trees and Call It PSA."
+
 Probability Types
 ========================================================
 

doc/references.rst

@@ -2,4 +2,14 @@
 References
 #############
 
-#. NRC NUREG-0492
+#. `NRC NUREG-0492 <http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0492/sr0492.pdf>`_
+#. `FTA: Concepts and Applications <http://www.hq.nasa.gov/office/codeq/risk/docs/ftacourse.pdf>`_
+#. `Fault Tree Handbook with Aerospace Applications <http://www.hq.nasa.gov/office/codeq/doctree/fthb.pdf>`_
+#. `Software Test Techniques for System Fault-Tree Analysis <http://http://www.cs.virginia.edu/~jck/publications/safecomp.97.pdf>`_
+#. D.Wakefield "You Can't Just Build Trees and Call It PSA"
+
+##############
+Web Resources
+##############
+
+#. `FTA Wiki Page <http://en.wikipedia.org/wiki/Fault_tree_analysis>`_

doc/scram_description.rst

@@ -75,11 +75,12 @@ EVENTS
     as a switch of True or False. Provides input to a logic gate.
     May be used to switch off a sub-tree.
 
-#. Conditioning Event :
+#. Conditional Event :
     Defines a specific condition or restriction
-    that apply to any logic gate. Used mostly with Priority AND,
+    that apply to any logic gate. Used mostly with Priority AND and
     Inhibit gates. The alternative name is a Conditional Qualifier.
-    Conditions may be abnormal cases or environment.
+    Conditions may be abnormal cases or environment. The probability
+    of this event might be a conditional probability.
 
 SYMBOLS
 -------
@@ -116,15 +117,17 @@ GATES
     simulated by chaining XOR gates if needed.
 
 #. Inhibit :
+    This gate is a special case of the AND gate.
     Output fault occurs if the single input fault occurs in the
     presense of an enabling condition (the enabling condition is
     represented by a Conditioning Event drawn to the right of the
-    gate.). Some packages restrict input events to only two events.
+    gate.). This gate restricts input events to only two events.
 
 #. Combination/VOTE :
     Output fault occurs if **m** out of the **n** input events
     occurs. The **m** input events need not to occur simultaneously. The output
-    occurs if at least **m** events occur.
+    occurs if at least **m** events occur. **m** is more than 1, and **n**
+    is more than **n**.
 
 #. NOT :
     Output fault occurs if the input event does not occur.

doc/todo.rst

@@ -28,6 +28,8 @@ Currently Low Hanging Fruits
 
 - Improve fault tree generator. *Low*
 
+- Implement Min-Cut-Upper Bound Approximation. *Moderate*
+
 
 Major Enhancements and Capabilities
 ===================================