the images should be written to the current directory ... -- Alex

[rrdtool.git] / doc / rrdgraph_rpn.pod

diff --git a/doc/rrdgraph_rpn.pod b/doc/rrdgraph_rpn.pod
index ff50865..dfc9a0b 100644 (file)
--- a/doc/rrdgraph_rpn.pod
+++ b/doc/rrdgraph_rpn.pod
@@ -1,4 +1,4 @@
-=head1 NAME  
+=head1 NAME
 
 rrdgraph_rpn - About RPN Math in rrdtool graph
 
@@ -15,11 +15,12 @@ takes as many elements from the stack as needed. Pushing is done
 implicitly, so whenever you specify a number or a variable, it gets
 pushed onto the stack automatically.
 
-At the end of the calculation there should be one and only one
-value left on the stack.  This is the outcome of the function and
-this is what is put into the I<vname>.  For B<CDEF> instructions,
-the stack is processed for each data point on the graph. B<VDEF>
-instructions work on an entire data set in one run.
+At the end of the calculation there should be one and only one value left on
+the stack.  This is the outcome of the function and this is what is put into
+the I<vname>.  For B<CDEF> instructions, the stack is processed for each
+data point on the graph. B<VDEF> instructions work on an entire data set in
+one run. Note, that currently B<VDEF> instructions only support a limited
+list of functions.
 
 Example: C<VDEF:maximum=mydata,MAXIMUM>
 
@@ -69,7 +70,7 @@ Z<>
 
 =item Comparing values
 
-B<MIN, MAX> 
+B<MIN, MAX>
 
 Pops two elements from the stack and returns the smaller or larger,
 respectively.  Note that I<infinite> is larger than anything else.
@@ -107,11 +108,24 @@ B<ATAN>
 
 Arctangent (output in radians).
 
+B<ATAN2>
+
+Arctangent of y,x components (output in radians).
+This pops one element from the stack, the x (cosine) component, and then
+a second, which is the y (sine) component.
+It then pushes the arctangent of their ratio, resolving the ambiguity between
+quadrants.
+
+Example: C<CDEF:angle=Y,X,ATAN2,RAD2DEG> will convert C<X,Y>
+components into an angle in degrees.
+
 B<FLOOR, CEIL>
 
 Round down or up to the nearest integer.
 
-Z<>
+B<DEG2RAD, RAD2DEG>
+
+Convert angle in degrees to radians, or radians to degrees.
 
 =item Set Operations
 
@@ -140,7 +154,7 @@ average is essentially computed as shown here:
                        delay     t0
                  <--------------->
                          delay       t1
-                     <--------------->  
+                     <--------------->
                               delay      t2
                          <--------------->
 
@@ -177,13 +191,11 @@ function cannot be used in B<VDEF> instructions.
 
 B<COUNT>
 
-Pushes the number 1 if this is the first value of the data set, the 
-number 2 if it is the second, and so on. This special value allows 
-you to make calculations based on the position of the value within 
+Pushes the number 1 if this is the first value of the data set, the
+number 2 if it is the second, and so on. This special value allows
+you to make calculations based on the position of the value within
 the data set. This function cannot be used in B<VDEF> instructions.
 
-Z<>
-
 =item Time
 
 Time inside RRDtool is measured in seconds since the epoch. The
@@ -217,7 +229,7 @@ Z<>
 
 =head1 VARIABLES
 
-These operators work only on B<VDEF> statements.
+These operators work only on B<VDEF> statements. Note that currently ONLY these work for B<VDEF>.
 
 =over 4
 
@@ -259,6 +271,18 @@ finite numbers and are always more than the I<Unknown> numbers.
 
 Example: C<VDEF:perc95=mydata,95,PERCENT>
 
+=item LSLSLOPE, LSLINT, LSLCORREL
+
+Return the parameters for a B<L>east B<S>quares B<L>ine I<(y = mx +b)> 
+which approximate the provided dataset.  LSLSLOPE is the slope I<(m)> of
+the line related to the COUNT position of the data.  LSLINT is the 
+y-intercept I<(b)>, which happens also to be the first data point on the 
+graph. LSLCORREL is the Correlation Coefficient (also know as Pearson's 
+Product Moment Correlation Coefficient).  It will range from 0 to +/-1 
+and represents the quality of fit for the approximation.   
+
+Example: C<VDEF:slope=mydata,LSLSLOPE>
+
 =back
 
 =head1 SEE ALSO