-=head1 NAME
+=head1 NAME
rrdgraph_rpn - About RPN Math in rrdtool graph
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 I<vname>. For B<CDEF> instructions,
-the stack is processed for each data point on the graph. B<VDEF>
-instructions work on an entire data set in one run.
+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 I<vname>. For B<CDEF> instructions, the stack is processed for each
+data point on the graph. B<VDEF> instructions work on an entire data set in
+one run. Note, that currently B<VDEF> instructions only support a limited
+list of functions.
Example: C<VDEF:maximum=mydata,MAXIMUM>
Example: C<CDEF:mydatabits=mydata,8,*>
This means: push variable I<mydata>, push the number 8, execute
-the operator I<+>. The operator needs two elements and uses those
+the operator I<*>. The operator needs two elements and uses those
to return one value. This value is then stored in I<mydatabits>.
As you may have guessed, this instruction means nothing more than
I<mydatabits = mydata * 8>. The real power of B<RPN> lies in the
=item Comparing values
-B<MIN, MAX>
+B<MIN, MAX>
Pops two elements from the stack and returns the smaller or larger,
-respectively. The two numbers shouldn't be I<infinite> or I<unknown>,
-if they are that value is pushed back onto the stack as the result.
-
-= for comment
-XXX What happens above if both a infinite and undefined value are on the
-XXX stack? Fritz
+respectively. Note that I<infinite> is larger than anything else.
+If one of the input numbers is I<unknown> then the result of the operation will be
+I<unknown> too.
B<LIMIT>
Add, subtract, multiply, divide, modulo
+B<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.
+
B<SIN, COS, LOG, EXP, SQRT>
Sine and cosine (input in radians), log and exp (natural logarithm),
Arctangent (output in radians).
+B<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: C<CDEF:angle=Y,X,ATAN2,RAD2DEG> will convert C<X,Y>
+components into an angle in degrees.
+
B<FLOOR, CEIL>
Round down or up to the nearest integer.
-Z<>
+B<DEG2RAD, RAD2DEG>
+
+Convert angle in degrees to radians, or radians to degrees.
+
+B<ABS>
+
+Take the absolute value.
=item Set Operations
compute the average of the values v1 to v6 after removing the smallest and
largest.
-B<TREND>
+B<AVG>
+
+Pop one element (I<count>) from the stack. Now pop I<count> elements and build the
+average, ignoring all UNKNOWN values in the process.
+
+Example: C<CDEF:x=a,b,c,d,4,AVG>
+
+B<TREND, TRENDNAN>
Create a "sliding window" average of another data series.
delay t0
<--------------->
delay t1
- <--------------->
+ <--------------->
delay t2
<--------------->
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.
+
+
=item Special values
B<UNKN>
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
+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. The
=head1 VARIABLES
-These operators work only on B<VDEF> statements.
+These operators work only on B<VDEF> statements. Note that currently ONLY these work for B<VDEF>.
=over 4
Example: C<VDEF:avg=mydata,AVERAGE>
+=item STDEV
+
+Returns the standard deviation of the values.
+
+Example: C<VDEF:stdev=mydata,STDEV>
+
=item LAST, FIRST
Return the last/first value including its time. The time for
Example: C<VDEF:perc95=mydata,95,PERCENT>
+=item LSLSLOPE, LSLINT, LSLCORREL
+
+Return the parameters for a B<L>east B<S>quares B<L>ine I<(y = mx +b)>
+which approximate the provided dataset. LSLSLOPE is the slope I<(m)> of
+the line related to the COUNT position of the data. LSLINT is the
+y-intercept I<(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: C<VDEF:slope=mydata,LSLSLOPE>
+
=back
=head1 SEE ALSO
=head1 AUTHOR
-Program by Tobias Oetiker E<lt>oetiker@ee.ethz.chE<gt>
+Program by Tobias Oetiker E<lt>tobi@oetiker.chE<gt>
This manual page by Alex van den Bogaerdt E<lt>alex@ergens.op.het.netE<gt>
projects / rrdtool.git / blobdiff