=include name
-=head1 SYNOPSYS
+=head1 SYNOPSIS
I<E<lt>RPN expressionE<gt>> :=
I<E<lt>vnameE<gt>>|I<E<lt>operatorE<gt>>|I<E<lt>valueE<gt>>
the stack is processed for each data point on the graph. B<VDEF>
instructions work on an entire data set in one run.
+Example: C<VDEF:maximum=mydata,MAXIMUM>
+
+This will set variable "maximum" which you now can use in the rest
+of your RRD script.
+
Example: C<CDEF:mydatabits=mydata,8,*>
This means: push variable I<mydata>, push the number 8, execute
Pops three elements from the stack. If the last element is 0 (false),
the first value is pushed back onto the stack, otherwise the second
popped value is pushed back. This does, indeed, mean that any value
-other than 0 is considered true.
-I<Note: Should this change? It should IMHO as all the other functions
-would return unknown if A,B or C were unknown>
+other than 0 is considered to be true.
Example: C<A,B,C,IF> should be read as C<if (A) then (B) else (C)>
Add, subtract, multiply, divide, modulo
-B<SIN, COS, LOG, EXP>
+B<SIN, COS, LOG, EXP, SQRT>
+
+Sine, cosine (input in radians), log, exp (natural logarithm), square root
-Sine, cosine (input in radians), log, exp (natural logarithm)
+B<ATAN>
+
+Arctangent. Output in radians.
B<FLOOR, CEIL>
Z<>
+=item Set Operations
+
+B<SORT, REV>
+
+Pop one element from the stack. This is the I<count> of items to be sorted
+(or reversed). The top I<count> of the remaining elements are then sorted
+(or reversed) in place on the stack.
+
+Example: C<CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/> will
+compute the average of the values v1..v6 after removing the smallest and
+largest.
+
+B<TREND>
+
+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)
+
=item Special values
B<UNKN>
Time inside RRDtool is measured in seconds since the epoch. This
epoch is defined to be S<C<Thu Jan 1 00:00:00 UTC 1970>>.
-Z<>
-
-=over 4
-
-=item NOW
+B<NOW>
Pushes the current time on the stack.
-Z<>
-
-=item TIME
+B<TIME>
Pushes the time the currently processed value was taken onto the stack.
-Z<>
-
-=item LTIME
+B<LTIME>
Takes the time as defined by B<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 on how to use this.
-=back
-
-For B<VDEF> operations, B<TIME> and B<LTIME> have a different meaning
-I<not yet implemented>. As the B<VDEF> statement does not work per
-value but rather on a complete time series, there is no such thing as
-the currently processed value. However, if you have used an operator
-that returned a time component and would like to have this available
-in the value component in stead (so you can use it as a number), you
-can use B<TIME> or B<LTIME> for that.
-
-Z<>
-
=item Processing the stack directly
B<DUP, POP, EXC>
Z<>
-=item Selecting characteristics
+=back
-These operators work only on B<VDEF> statements.
-I<We can make most of them work at DEF and CDEF statements. If we do
-so, we have a moving (not rolling!) average, max,min etcetera>
+=head1 VARIABLES
-Z<>
+These operators work only on B<VDEF> statements.
=over 4
=item MAXIMUM, MINIMUM, AVERAGE
Return the corresponding value, MAXIMUM and MINIMUM also return
-the first occurance of that value in the time component.
+the first occurrence of that value in the time component.
Example: C<VDEF:avg=mydata,AVERAGE>
-Z<>
-
=item LAST, FIRST
Return the last,first value including its time. The time for
FIRST is actually the start of the corresponding interval, where
-LASTs time component returns the end of the corresponding interval.
+the LAST time component returns the end of the corresponding interval.
Example: C<VDEF:first=mydata,FIRST>
-Z<>
-
=item TOTAL
-Returns the rate from each defined timeslot multiplied with the
+Returns the rate from each defined time slot multiplied with the
step size. This can for instance return total bytes transfered
when you have logged bytes per second. The time component returns
the amount of seconds
Example: C<VDEF:total=mydata,TOTAL>
-Z<>
-
=item PERCENT
Should follow a B<DEF> or B<CDEF> I<vname>. This I<vname> is popped,
purpose so if this operator returns an I<unknown> you have quite a lot
of them in your data. B<Inf>inite numbers are lesser, or more, than the
finite numbers and are always more than the I<Unknown> numbers.
+(NaN E<lt> -INF E<lt> finite values E<lt> INF)
Example: C<VDEF:perc95=mydata,95,PERCENT>
=back
-=back
-
=include see_also
projects / rrdtool.git / blobdiff