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CentOS 7.0 - man page for rrdgraph_rpn (centos section 1)

RRDGRAPH_RPN(1) 			     rrdtool				  RRDGRAPH_RPN(1)

NAME
       rrdgraph_rpn - About RPN Math in rrdtool graph

SYNOPSIS
       RPN expression:=vname|operator|value[,RPN expression]

DESCRIPTION
       If you have ever used a traditional HP calculator you already know RPN (Reverse Polish
       Notation).  The idea behind RPN 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 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 vname.  For CDEF
       instructions, the stack is processed for each data point on the graph. VDEF instructions
       work on an entire data set in one run. Note, that currently VDEF instructions only support
       a limited list of functions.

       Example: "VDEF:maximum=mydata,MAXIMUM"

       This will set variable "maximum" which you now can use in the rest of your RRD script.

       Example: "CDEF:mydatabits=mydata,8,*"

       This means:  push variable mydata, push the number 8, execute the operator *. The operator
       needs two elements and uses those to return one value.  This value is then stored in
       mydatabits.  As you may have guessed, this instruction means nothing more than mydatabits
       = mydata * 8.  The real power of RPN lies in the fact that it is always clear in which
       order to process the input.  For expressions like "a = b + 3 * 5" you need to multiply 3
       with 5 first before you add b to get a. However, with parentheses you could change this
       order: "a = (b + 3) * 5". In RPN, you would do "a = b, 3, +, 5, *" without the need for
       parentheses.

OPERATORS
       Boolean operators
	   LT, LE, GT, GE, EQ, NE

	   Pop two elements from the stack, compare them for the selected condition and return 1
	   for true or 0 for false. Comparing an unknown or an infinite value will result in
	   unknown returned ... which will also be treated as false by the IF call.

	   UN, ISINF

	   Pop one element from the stack, compare this to unknown respectively to positive or
	   negative infinity. Returns 1 for true or 0 for false.

	   IF

	   Pops three elements from the stack.	If the element popped last is 0 (false), the
	   value popped first is pushed back onto the stack, otherwise the value popped second is
	   pushed back. This does, indeed, mean that any value other than 0 is considered to be
	   true.

	   Example: "A,B,C,IF" should be read as "if (A) then (B) else (C)"

       Comparing values
	   MIN, MAX

	   Pops two elements from the stack and returns the smaller or larger, respectively.
	   Note that infinite is larger than anything else.  If one of the input numbers is
	   unknown then the result of the operation will be unknown too.

	   LIMIT

	   Pops two elements from the stack and uses them to define a range.  Then it pops
	   another element and if it falls inside the range, it is pushed back. If not, an
	   unknown is pushed.

	   The range defined includes the two boundaries (so: a number equal to one of the
	   boundaries will be pushed back). If any of the three numbers involved is either
	   unknown or infinite this function will always return an unknown

	   Example: "CDEF:a=alpha,0,100,LIMIT" will return unknown if alpha is lower than 0 or if
	   it is higher than 100.

       Arithmetics
	   +, -, *, /, %

	   Add, subtract, multiply, divide, modulo

	   ADDNAN

	   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.

	   SIN, COS, LOG, EXP, SQRT

	   Sine and cosine (input in radians), log and exp (natural logarithm), square root.

	   ATAN

	   Arctangent (output in radians).

	   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: "CDEF:angle=Y,X,ATAN2,RAD2DEG" will convert "X,Y" components into an angle in
	   degrees.

	   FLOOR, CEIL

	   Round down or up to the nearest integer.

	   DEG2RAD, RAD2DEG

	   Convert angle in degrees to radians, or radians to degrees.

	   ABS

	   Take the absolute value.

       Set Operations
	   SORT, REV

	   Pop one element from the stack.  This is the count of items to be sorted (or
	   reversed).  The top count of the remaining elements are then sorted (or reversed) in
	   place on the stack.

	   Example: "CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/" will compute the
	   average of the values v1 to v6 after removing the smallest and largest.

	   AVG

	   Pop one element (count) from the stack. Now pop count elements and build the average,
	   ignoring all UNKNOWN values in the process.

	   Example: "CDEF:x=a,b,c,d,4,AVG"

	   TREND, TRENDNAN

	   Create a "sliding window" average of another data series.

	   Usage: CDEF:smoothed=x,1800,TREND

	   This will create a half-hour (1800 second) sliding window average of x.  The average
	   is essentially computed as shown here:

			    +---!---!---!---!---!---!---!---!--->
								now
				  delay     t0
			    <--------------->
				    delay	t1
				<--------------->
					 delay	    t2
				    <--------------->

		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)

	   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.

	   PREDICT, PREDICTSIGMA

	   Create a "sliding window" average/sigma of another data series, that also shifts the
	   data series by given amounts of of time as well

	   Usage - explicit stating shifts: CDEF:predict=<shift n>,...,<shift
	   1>,n,<window>,x,PREDICT CDEF:sigma=<shift n>,...,<shift 1>,n,<window>,x,PREDICTSIGMA

	   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

	   Example: CDEF:predict=172800,86400,2,1800,x,PREDICT

	   This will create a half-hour (1800 second) sliding window average/sigma of x, that
	   average is essentially computed as shown here:

	    +---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!--->
										now
							     shift 1	    t0
						    <----------------------->
					  window
				    <--------------->
						  shift 2
			    <----------------------------------------------->
		  window
	    <--------------->
								 shift 1	t1
							<----------------------->
					      window
					<--------------->
						       shift 2
				<----------------------------------------------->
		      window
		<--------------->

	    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)

	   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...

	   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.

	   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

	   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.

	   This prediction can only be used for short term extrapolations - say a few days into
	   the future-

       Special values
	   UNKN

	   Pushes an unknown value on the stack

	   INF, NEGINF

	   Pushes a positive or negative infinite value on the stack. When such a value is
	   graphed, it appears at the top or bottom of the graph, no matter what the actual value
	   on the y-axis is.

	   PREV

	   Pushes an unknown value if this is the first value of a data set or otherwise the
	   result of this CDEF at the previous time step. This allows you to do calculations
	   across the data.  This function cannot be used in VDEF instructions.

	   PREV(vname)

	   Pushes an unknown value if this is the first value of a data set or otherwise the
	   result of the vname variable at the previous time step. This allows you to do
	   calculations across the data. This function cannot be used in VDEF instructions.

	   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 the data set. This function cannot be used in VDEF
	   instructions.

       Time
	   Time inside RRDtool is measured in seconds since the epoch. The epoch is defined to be
	   "Thu Jan  1 00:00:00 UTC 1970".

	   NOW

	   Pushes the current time on the stack.

	   TIME

	   Pushes the time the currently processed value was taken at onto the stack.

	   LTIME

	   Takes the time as defined by TIME, applies the time zone offset valid at that time
	   including daylight saving time if your OS supports it, and pushes the result on the
	   stack.  There is an elaborate example in the examples section below on how to use
	   this.

       Processing the stack directly
	   DUP, POP, EXC

	   Duplicate the top element, remove the top element, exchange the two top elements.

VARIABLES
       These operators work only on VDEF statements. Note that currently ONLY these work for
       VDEF.

       MAXIMUM, MINIMUM, AVERAGE
	   Return the corresponding value, MAXIMUM and MINIMUM also return the first occurrence
	   of that value in the time component.

	   Example: "VDEF:avg=mydata,AVERAGE"

       STDEV
	   Returns the standard deviation of the values.

	   Example: "VDEF:stdev=mydata,STDEV"

       LAST, FIRST
	   Return the last/first non-nan or infinite value for the selected data stream,
	   including its timestamp.

	   Example: "VDEF:first=mydata,FIRST"

       TOTAL
	   Returns the rate from each defined time slot multiplied with the 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.

	   Example: "VDEF:total=mydata,TOTAL"

       PERCENT, PERCENTNAN
	   This should follow a DEF or CDEF vname. The vname 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 percentage percent of the values is lower or equal than
	   the result.	For PERCENTNAN Unknown values are ignored, but for PERCENT Unknown values
	   are considered lower than any finite number for this purpose so if this operator
	   returns an unknown you have quite a lot of them in your data.  Infinite numbers are
	   lesser, or more, than the finite numbers and are always more than the Unknown numbers.
	   (NaN < -INF < finite values < INF)

	   Example: "VDEF:perc95=mydata,95,PERCENT"
		    "VDEF:percnan95=mydata,95,PERCENTNAN"

       LSLSLOPE, LSLINT, LSLCORREL
	   Return the parameters for a Least Squares Line (y = mx +b) which approximate the
	   provided dataset.  LSLSLOPE is the slope (m) of the line related to the COUNT position
	   of the data.  LSLINT is the y-intercept (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: "VDEF:slope=mydata,LSLSLOPE"

SEE ALSO
       rrdgraph gives an overview of how rrdtool graph works.  rrdgraph_data describes DEF,CDEF
       and VDEF in detail.  rrdgraph_rpn describes the RPN language used in the ?DEF statements.
       rrdgraph_graph page describes all of the graph and print functions.

       Make sure to read rrdgraph_examples for tips&tricks.

AUTHOR
       Program by Tobias Oetiker <tobi@oetiker.ch>

       This manual page by Alex van den Bogaerdt <alex@vandenbogaerdt.nl> with corrections and/or
       additions by several people

1.4.8					    2013-05-23				  RRDGRAPH_RPN(1)


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All times are GMT -4. The time now is 02:17 AM.

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