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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>
<p>Pop two elements from the stack, compare them for the selected condition
and return 1 for true or 0 for false. Comparing an <em>unknown</em> or an
-<em>infinite</em> value will always result in 0 (false).</p>
+<em>infinite</em> value will result in <em>unknown</em> returned ... which will also be
+treated as false by the <strong>IF</strong> call.</p>
<p><strong>UN, ISINF</strong></p>
<p>Pop one element from the stack, compare this to <em>unknown</em> respectively
to <em>positive or negative infinity</em>. Returns 1 for true or 0 for false.</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>
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><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>
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, TRENDNAN</strong></p>
-<p>Create a ``sliding window'' average of another data series.</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
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 behavior. 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>
<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_stdev">STDEV</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="item_last_2c_first">LAST, FIRST</a></strong></dt>
+<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
-FIRST is actually the start of the corresponding interval, whereas
-LAST returns the end of the corresponding interval.</p>
+<p>Return the last/first non-nan or infinite value for the selected data
+stream, including its timestamp.</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
-step size. This can, for instance, return total bytes transfered
+step size. This can, for instance, return total bytes transferred
when you have logged bytes per second. The time component returns
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>