yet another try to get the rpn example right ... #246

[rrdtool.git] / doc / rpntutorial.pod

diff --git a/doc/rpntutorial.pod b/doc/rpntutorial.pod
index 9829eb8..0ab3131 100644 (file)
--- a/doc/rpntutorial.pod
+++ b/doc/rpntutorial.pod
@@ -2,8 +2,6 @@
 
 rpntutorial - Reading RRDtool RPN Expressions by Steve Rader
 
-=for html <div align="right"><a href="rpntutorial.pdf">PDF</a> version.</div>
-
 =head1 DESCRIPTION
 
 This tutorial should help you get to grips with RRDtool RPN expressions
@@ -26,7 +24,7 @@ RPN expression 2,1,GT evaluates to 1.
 
 Now consider "2,1,LE".  This RPN expression could be read as "is
 two less than or equal to one?".   The natural response is "no"
-and thus the RPN expression 2,1,LE evaluates to 0. 
+and thus the RPN expression 2,1,LE evaluates to 0.
 
 =head1 Reading the IF Operator
 
@@ -57,7 +55,7 @@ GT, GE and EQ operators.
 
 While compound expressions can look overly complex, they can be
 considered elegantly simple.  To quickly comprehend RPN expressions,
-you must know the the algorithm for evaluating RPN expressions:
+you must know the algorithm for evaluating RPN expressions:
 iterate searches from the left to the right looking for an operator.
 When it's found, apply that operator by popping the operator and some
 number of values (and by definition, not operators) off the stack.
@@ -78,7 +76,7 @@ with multiple logic operators:
  1) 20,10,GT,10,20,IF  eval is 20,10,GT = 1     result is 1,10,20,IF
 
 read the eval as pop "20 is greater than 10" so push 1
- 
+
  2) 1,10,20,IF         eval is 1,10,20,IF = 10  result is 10
 
 read pop "if 1 then 10 else 20" so push 10.  Only 10 is left so
@@ -88,27 +86,22 @@ Let's read a complex RPN expression that also has the traditional
 multiplication operator:
 
  1) 128,8,*,7000,GT,7000,128,8,*,IF  eval 128,8,*       result is 1024
- 2) 1024,7000,GT,7000,128,8,*,IF     eval 1024,7000,GT  result is 0
- 3) 0,128,8,*,IF                     eval 128,8,*       result is 1024
- 4) 0,7000,1024,IF                                      result is 1024
-
+ 2) 1024   ,7000,GT,7000,128,8,*,IF  eval 1024,7000,GT  result is 0
+ 3) 0,              7000,128,8,*,IF  eval 128,8,*       result is 1024
+ 4) 0,              7000,1024,   IF                     result is 1024
 
 Now let's go back to the first example of multiple logic operators,
 but replace the value 20 with the variable "input":
 
-=for comment
-XXX wo kommt das A ploetzlich her? Hier braucht es einen Satz, dass A als
-XXX placeholder  zum Lesbarmachen verwendet wird (shortcut).
-
- 1) input,10,GT,10,input,IF  eval is input,10,GT  result is A
+ 1) input,10,GT,10,input,IF  eval is input,10,GT  ( lets call this A )
 
 Read eval as "if input > 10 then true" and replace "input,10,GT"
 with "A":
-  
+
  2) A,10,input,IF            eval is A,10,input,IF
 
 read "if A then 10 else input".  Now replace A with it's verbose
-description againg and--voila!--you have a easily readable description
+description again and--voila!--you have an easily readable description
 of the expression:
 
  if input > 10 then 10 else input
@@ -145,7 +138,7 @@ traditional notation.  Explain why they have different answers.
 Answer 1:
 
     3*2+1 = 7 and 3*(2+1) = 9.  These expressions have
-    different answers because the altering of the plus and 
+    different answers because the altering of the plus and
     times operators alter the order of their evaluation.