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+++ b/doc/rrdgraph_rpn.html
<body style="background-color: white">
-<p><a name="__index__"></a></p>
+
<!-- INDEX BEGIN -->
+<div name="index">
+<p><a name="__index__"></a></p>
<!--
<ul>
<li><a href="#see_also">SEE ALSO</a></li>
<li><a href="#author">AUTHOR</a></li>
</ul>
+
-->
+
+
+</div>
<!-- INDEX END -->
<p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>If you have ever used a traditional HP calculator you already know
-<strong>RPN</strong>. The idea behind <strong>RPN</strong> is that you have a stack and push
+<strong>RPN</strong> (Reverse Polish Notation).
+The idea behind <strong>RPN</strong> is that you have a stack and push
your data onto this stack. Whenever you execute an operation, it
takes as many elements from the stack as needed. Pushing is done
implicitly, so whenever you specify a number or a variable, it gets
one run. Note, that currently <strong>VDEF</strong> instructions only support a limited
list of functions.</p>
<p>Example: <code>VDEF:maximum=mydata,MAXIMUM</code></p>
-<p>This will set variable ``maximum'' which you now can use in the rest
+<p>This will set variable "maximum" which you now can use in the rest
of your RRD script.</p>
<p>Example: <code>CDEF:mydatabits=mydata,8,*</code></p>
<p>This means: push variable <em>mydata</em>, push the number 8, execute
<hr />
<h1><a name="operators">OPERATORS</a></h1>
<dl>
-<dt><strong><a name="item_boolean_operators">Boolean operators</a></strong></dt>
+<dt><strong><a name="boolean_operators" class="item">Boolean operators</a></strong></dt>
<dd>
<p><strong>LT, LE, GT, GE, EQ, NE</strong></p>
otherwise the value popped second is pushed back. This does, indeed,
mean that any value other than 0 is considered to be true.</p>
<p>Example: <code>A,B,C,IF</code> should be read as <code>if (A) then (B) else (C)</code></p>
+<p></p>
</dd>
-<dt><strong><a name="item_comparing_values">Comparing values</a></strong></dt>
+<dt><strong><a name="comparing_values" class="item">Comparing values</a></strong></dt>
<dd>
<p><strong>MIN, MAX</strong></p>
@@ -105,12 +113,16 @@ numbers involved is either <em>unknown</em> or <em>infinite</em> this function
will always return an <em>unknown</em></p>
<p>Example: <code>CDEF:a=alpha,0,100,LIMIT</code> will return <em>unknown</em> if
alpha is lower than 0 or if it is higher than 100.</p>
+<p></p>
</dd>
-<dt><strong><a name="item_arithmetics">Arithmetics</a></strong></dt>
+<dt><strong><a name="arithmetics" class="item">Arithmetics</a></strong></dt>
<dd>
<p><strong>+, -, *, /, %</strong></p>
<p>Add, subtract, multiply, divide, modulo</p>
+<p><strong>ADDNAN</strong></p>
+<p>NAN-safe addition. If one parameter is NAN/UNKNOWN it'll be treated as
+zero. If both parameters are NAN/UNKNOWN, NAN/UNKNOWN will be returned.</p>
<p><strong>SIN, COS, LOG, EXP, SQRT</strong></p>
<p>Sine and cosine (input in radians), log and exp (natural logarithm),
square root.</p>
<p><strong>ABS</strong></p>
<p>Take the absolute value.</p>
</dd>
-<dt><strong><a name="item_set_operations">Set Operations</a></strong></dt>
+<dt><strong><a name="set_operations" class="item">Set Operations</a></strong></dt>
<dd>
<p><strong>SORT, REV</strong></p>
<p>Pop one element (<em>count</em>) from the stack. Now pop <em>count</em> elements and build the
average, ignoring all UNKNOWN values in the process.</p>
<p>Example: <code>CDEF:x=a,b,c,d,4,AVG</code></p>
-<p><strong>TREND</strong></p>
-<p>Create a ``sliding window'' average of another data series.</p>
+<p><strong>TREND, TRENDNAN</strong></p>
+<p>Create a "sliding window" average of another data series.</p>
<p>Usage:
CDEF:smoothed=x,1800,TREND</p>
<p>This will create a half-hour (1800 second) sliding window average of x. The
Value at sample (t0) will be the average between (t0-delay) and (t0)
Value at sample (t1) will be the average between (t1-delay) and (t1)
Value at sample (t2) will be the average between (t2-delay) and (t2)</pre>
+<p>TRENDNAN is - in contrast to TREND - NAN-safe. If you use TREND and one
+source value is NAN the complete sliding window is affected. The TRENDNAN
+operation ignores all NAN-values in a sliding window and computes the
+average of the remaining values.</p>
+<p><strong>PREDICT, PREDICTSIGMA</strong></p>
+<p>Create a "sliding window" average/sigma of another data series, that also
+shifts the data series by given amounts of of time as well</p>
+<p>Usage - explicit stating shifts:
+CDEF:predict=<shift n>,...,<shift 1>,n,<window>,x,PREDICT
+CDEF:sigma=<shift n>,...,<shift 1>,n,<window>,x,PREDICTSIGMA</p>
+<p>Usage - shifts defined as a base shift and a number of time this is applied
+CDEF:predict=<shift multiplier>,-n,<window>,x,PREDICT
+CDEF:sigma=<shift multiplier>,-n,<window>,x,PREDICTSIGMA</p>
+<p>Example:
+CDEF:predict=172800,86400,2,1800,x,PREDICT</p>
+<p>This will create a half-hour (1800 second) sliding window average/sigma of x, that
+average is essentially computed as shown here:</p>
+<pre>
+ +---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!--->
+ now
+ shift 1 t0
+ <----------------------->
+ window
+ <--------------->
+ shift 2
+ <----------------------------------------------->
+ window
+ <--------------->
+ shift 1 t1
+ <----------------------->
+ window
+ <--------------->
+ shift 2
+ <----------------------------------------------->
+ window
+ <---------------></pre>
+<pre>
+ Value at sample (t0) will be the average between (t0-shift1-window) and (t0-shift1)
+ and between (t0-shift2-window) and (t0-shift2)
+ Value at sample (t1) will be the average between (t1-shift1-window) and (t1-shift1)
+ and between (t1-shift2-window) and (t1-shift2)</pre>
+<p>The function is by design NAN-safe.
+This also allows for extrapolation into the future (say a few days)
+- you may need to define the data series whit the optional start= parameter, so that
+the source data series has enough data to provide prediction also at the beginning of a graph...</p>
+<p>Here an example, that will create a 10 day graph that also shows the
+prediction 3 days into the future with its uncertainty value (as defined by avg+-4*sigma)
+This also shows if the prediction is exceeded at a certain point.</p>
+<p>rrdtool graph image.png --imgformat=PNG \
+ --start=-7days --end=+3days --width=1000 --height=200 --alt-autoscale-max \
+ DEF:value=value.rrd:value:AVERAGE:start=-14days \
+ LINE1:value#ff0000:value \
+ CDEF:predict=86400,-7,1800,value,PREDICT \
+ CDEF:sigma=86400,-7,1800,value,PREDICTSIGMA \
+ CDEF:upper=predict,sigma,3,*,+ \
+ CDEF:lower=predict,sigma,3,*,- \
+ LINE1:predict#00ff00:prediction \
+ LINE1:upper#0000ff:upper\ certainty\ limit \
+ LINE1:lower#0000ff:lower\ certainty\ limit \
+ CDEF:exceeds=value,UN,0,value,lower,upper,LIMIT,UN,IF \
+ TICK:exceeds#aa000080:1</p>
+<p>Note: Experience has shown that a factor between 3 and 5 to scale sigma is a good
+discriminator to detect abnormal behaviour. This obviously depends also on the type
+of data and how "noisy" the data series is.</p>
+<p>This prediction can only be used for short term extrapolations - say a few days into the future-</p>
</dd>
-<dt><strong><a name="item_special_values">Special values</a></strong></dt>
+<dt><strong><a name="special_values" class="item">Special values</a></strong></dt>
<dd>
<p><strong>UNKN</strong></p>
you to make calculations based on the position of the value within
the data set. This function cannot be used in <strong>VDEF</strong> instructions.</p>
</dd>
-<dt><strong><a name="item_time">Time</a></strong></dt>
+<dt><strong><a name="time" class="item">Time</a></strong></dt>
<dd>
<p>Time inside RRDtool is measured in seconds since the epoch. The
it, and pushes the result on the stack. There is an elaborate example
in the examples section below on how to use this.</p>
</dd>
-<dt><strong><a name="item_processing_the_stack_directly">Processing the stack directly</a></strong></dt>
+<dt><strong><a name="processing_the_stack_directly" class="item">Processing the stack directly</a></strong></dt>
<dd>
<p><strong>DUP, POP, EXC</strong></p>
<p>Duplicate the top element, remove the top element, exchange the two
top elements.</p>
+<p></p>
</dd>
</dl>
<p>
<h1><a name="variables">VARIABLES</a></h1>
<p>These operators work only on <strong>VDEF</strong> statements. Note that currently ONLY these work for <strong>VDEF</strong>.</p>
<dl>
-<dt><strong><a name="item_maximum_2c_minimum_2c_average">MAXIMUM, MINIMUM, AVERAGE</a></strong></dt>
+<dt><strong><a name="maximum_minimum_average" class="item">MAXIMUM, MINIMUM, AVERAGE</a></strong></dt>
<dd>
<p>Return the corresponding value, MAXIMUM and MINIMUM also return
the first occurrence of that value in the time component.</p>
<p>Example: <code>VDEF:avg=mydata,AVERAGE</code></p>
</dd>
-<dt><strong><a name="item_last_2c_first">LAST, FIRST</a></strong></dt>
+<dt><strong><a name="stdev" class="item">STDEV</a></strong></dt>
+
+<dd>
+<p>Returns the standard deviation of the values.</p>
+<p>Example: <code>VDEF:stdev=mydata,STDEV</code></p>
+</dd>
+<dt><strong><a name="last_first" class="item">LAST, FIRST</a></strong></dt>
<dd>
<p>Return the last/first value including its time. The time for
LAST returns the end of the corresponding interval.</p>
<p>Example: <code>VDEF:first=mydata,FIRST</code></p>
</dd>
-<dt><strong><a name="item_total">TOTAL</a></strong></dt>
+<dt><strong><a name="total" class="item">TOTAL</a></strong></dt>
<dd>
<p>Returns the rate from each defined time slot multiplied with the
the number of seconds.</p>
<p>Example: <code>VDEF:total=mydata,TOTAL</code></p>
</dd>
-<dt><strong><a name="item_percent">PERCENT</a></strong></dt>
+<dt><strong><a name="percent_percentnan" class="item">PERCENT, PERCENTNAN</a></strong></dt>
<dd>
<p>This should follow a <strong>DEF</strong> or <strong>CDEF</strong> <em>vname</em>. The <em>vname</em> is popped,
another number is popped which is a certain percentage (0..100). The
data set is then sorted and the value returned is chosen such that
<em>percentage</em> percent of the values is lower or equal than the result.
+For PERCENTNAN <em>Unknown</em> values are ignored, but for PERCENT
<em>Unknown</em> values are considered lower than any finite number for this
purpose so if this operator returns an <em>unknown</em> you have quite a lot
of them in your data. <strong>Inf</strong>inite numbers are lesser, or more, than the
finite numbers and are always more than the <em>Unknown</em> numbers.
(NaN < -INF < finite values < INF)</p>
-<p>Example: <code>VDEF:perc95=mydata,95,PERCENT</code></p>
+<p>Example: <code>VDEF:perc95=mydata,95,PERCENT</code>
+ <code>VDEF:percnan95=mydata,95,PERCENTNAN</code></p>
</dd>
-<dt><strong><a name="item_lslslope_2c_lslint_2c_lslcorrel">LSLSLOPE, LSLINT, LSLCORREL</a></strong></dt>
+<dt><strong><a name="lslslope_lslint_lslcorrel" class="item">LSLSLOPE, LSLINT, LSLCORREL</a></strong></dt>
<dd>
<p>Return the parameters for a <strong>L</strong>east <strong>S</strong>quares <strong>L</strong>ine <em>(y = mx +b)</em>
<hr />
<h1><a name="author">AUTHOR</a></h1>
<p>Program by Tobias Oetiker <<a href="mailto:tobi@oetiker.ch">tobi@oetiker.ch</a>></p>
-<p>This manual page by Alex van den Bogaerdt <<a href="mailto:alex@ergens.op.het.net">alex@ergens.op.het.net</a>></p>
+<p>This manual page by Alex van den Bogaerdt <<a href="mailto:alex@vandenbogaerdt.nl">alex@vandenbogaerdt.nl</a>>
+with corrections and/or additions by several people</p>
</body>