=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
B<LT, LE, GT, GE, EQ, NE>
-I<Note: NE is not yet implemented>
-
Pop two elements from the stack, compare them for the selected condition
and return 1 for true or 0 for false. Comparing an I<unknown> or an
I<infinite> value will always result in 0 (false).
B<UN, ISINF>
-I<Note: ISINF is not yet implemented>
-
Pop one element from the stack, compare this to I<unknown> respectively
to I<positive or negative infinity>. Returns 1 for true or 0 for false.
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
+
+B<ATAN>
-Sine, cosine (input in radians), log, exp (natural logarithm)
+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>
step. This allows you to do calculations across the data. This
function cannot be used in B<VDEF> instructions.
+B<PREV(vname)>
+
+Pushes an I<unknown> value if this is the first value of a data
+set or otherwise the result of vname variable at the previous time
+step. This allows you to do calculations across the data. This
+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
+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. 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
+Return the corresponding value, MAXIMUM and MINIMUM also return
+the first occurrence of that value in the time component.
-Z<>
+Example: C<VDEF:avg=mydata,AVERAGE>
=item LAST, FIRST
-Return the last,first value including its time
+Return the last,first value including its time. The time for
+FIRST is actually the start of the corresponding interval, where
+the LAST time component returns the end of the corresponding interval.
-Z<>
+Example: C<VDEF:first=mydata,FIRST>
+
+=item TOTAL
+
+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
-=item PERCENTILE
+Example: C<VDEF:total=mydata,TOTAL>
+
+=item PERCENT
Should follow a B<DEF> or B<CDEF> I<vname>. This I<vname> is popped,
another number is popped which is a certain percentage (0..100). The
I<percentage> percent of the values is lower or equal than the result.
I<Unknown> values are considered lower than any finite number for this
purpose so if this operator returns an I<unknown> you have quite a lot
-of them in your data...
-
-Example: C<VDEF:perc95=95,mydata,PERCENTILE>
+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)
-=back
+Example: C<VDEF:perc95=mydata,95,PERCENT>
=back
projects / rrdtool.git / blobdiff