1 RRDGRAPH_RPN(1) rrdtool RRDGRAPH_RPN(1)
6 rrdgraph_rpn - About RPN Math in rrdtool graph
9 _\bR_\bP_\bN _\be_\bx_\bp_\br_\be_\bs_\bs_\bi_\bo_\bn:=_\bv_\bn_\ba_\bm_\be|_\bo_\bp_\be_\br_\ba_\bt_\bo_\br|_\bv_\ba_\bl_\bu_\be[,_\bR_\bP_\bN _\be_\bx_\bp_\br_\be_\bs_\bs_\bi_\bo_\bn]
14 this stack. Whenever you execute an operation, it takes as many ele-
15 ments from the stack as needed. Pushing is done implicitly, so whenever
16 you specify a number or a variable, it gets pushed onto the stack auto-
17 matically.
19 At the end of the calculation there should be one and only one value
20 left on the stack. This is the outcome of the function and this is
24 support a limited list of functions.
26 Example: "VDEF:maximum=mydata,MAXIMUM"
28 This will set variable "maximum" which you now can use in the rest of
29 your RRD script.
31 Example: "CDEF:mydatabits=mydata,8,*"
34 ator _\b*. The operator needs two elements and uses those to return one
36 guessed, this instruction means nothing more than _\bm_\by_\bd_\ba_\bt_\ba_\bb_\bi_\bt_\bs _\b= _\bm_\by_\bd_\ba_\bt_\ba _\b*
38 which order to process the input. For expressions like "a = b + 3 * 5"
40 with parentheses you could change this order: "a = (b + 3) * 5". In
44 Boolean operators
47 Pop two elements from the stack, compare them for the selected con-
54 tively to _\bp_\bo_\bs_\bi_\bt_\bi_\bv_\be _\bo_\br _\bn_\be_\bg_\ba_\bt_\bi_\bv_\be _\bi_\bn_\bf_\bi_\bn_\bi_\bt_\by. Returns 1 for true or 0
55 for false.
59 Pops three elements from the stack. If the element popped last is
60 0 (false), the value popped first is pushed back onto the stack,
61 otherwise the value popped second is pushed back. This does,
62 indeed, mean that any value other than 0 is considered to be true.
64 Example: "A,B,C,IF" should be read as "if (A) then (B) else (C)"
68 Comparing values
71 Pops two elements from the stack and returns the smaller or larger,
78 Pops two elements from the stack and uses them to define a range.
79 Then it pops another element and if it falls inside the range, it
82 The range defined includes the two boundaries (so: a number equal
83 to one of the boundaries will be pushed back). If any of the three
84 numbers involved is either _\bu_\bn_\bk_\bn_\bo_\bw_\bn or _\bi_\bn_\bf_\bi_\bn_\bi_\bt_\be this function will
88 lower than 0 or if it is higher than 100.
92 Arithmetics
95 Add, subtract, multiply, divide, modulo
99 NAN-safe addition. If one parameter is NAN/UNKNOWN it'll be treated
100 as zero. If both parameters are NAN/UNKNOWN, NAN/UNKNOWN will be
101 returned.
105 Sine and cosine (input in radians), log and exp (natural loga-
106 rithm), square root.
110 Arctangent (output in radians).
114 Arctangent of y,x components (output in radians). This pops one
115 element from the stack, the x (cosine) component, and then a sec-
116 ond, which is the y (sine) component. It then pushes the arctan-
117 gent of their ratio, resolving the ambiguity between quadrants.
119 Example: "CDEF:angle=Y,X,ATAN2,RAD2DEG" will convert "X,Y" compo-
120 nents into an angle in degrees.
124 Round down or up to the nearest integer.
128 Convert angle in degrees to radians, or radians to degrees.
132 Take the absolute value.
134 Set Operations
139 then sorted (or reversed) in place on the stack.
141 Example: "CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/"
142 will compute the average of the values v1 to v6 after removing the
143 smallest and largest.
147 Pop one element (_\bc_\bo_\bu_\bn_\bt) from the stack. Now pop _\bc_\bo_\bu_\bn_\bt elements and
148 build the average, ignoring all UNKNOWN values in the process.
150 Example: "CDEF:x=a,b,c,d,4,AVG"
154 Create a "sliding window" average of another data series.
156 Usage: CDEF:smoothed=x,1800,TREND
158 This will create a half-hour (1800 second) sliding window average
159 of x. The average is essentially computed as shown here:
161 +---!---!---!---!---!---!---!---!--->
162 now
163 delay t0
164 <--------------->
165 delay t1
166 <--------------->
167 delay t2
168 <--------------->
170 Value at sample (t0) will be the average between (t0-delay) and (t0)
171 Value at sample (t1) will be the average between (t1-delay) and (t1)
172 Value at sample (t2) will be the average between (t2-delay) and (t2)
174 TRENDNAN is - in contrast to TREND - NAN-safe. If you use TREND and
175 one source value is NAN the complete sliding window is affected.
176 The TRENDNAN operation ignores all NAN-values in a sliding window
177 and computes the average of the remaining values.
179 Special values
182 Pushes an unknown value on the stack
186 Pushes a positive or negative infinite value on the stack. When
187 such a value is graphed, it appears at the top or bottom of the
188 graph, no matter what the actual value on the y-axis is.
194 allows you to do calculations across the data. This function can-
200 otherwise the result of the vname variable at the previous time
201 step. This allows you to do calculations across the data. This
206 Pushes the number 1 if this is the first value of the data set, the
207 number 2 if it is the second, and so on. This special value allows
208 you to make calculations based on the position of the value within
211 Time
212 Time inside RRDtool is measured in seconds since the epoch. The
213 epoch is defined to be "Thu Jan 1 00:00:00 UTC 1970".
217 Pushes the current time on the stack.
221 Pushes the time the currently processed value was taken at onto the
222 stack.
227 valid at that time including daylight saving time if your OS sup-
228 ports it, and pushes the result on the stack. There is an elabo-
229 rate example in the examples section below on how to use this.
231 Processing the stack directly
234 Duplicate the top element, remove the top element, exchange the two
235 top elements.
243 MAXIMUM, MINIMUM, AVERAGE
244 Return the corresponding value, MAXIMUM and MINIMUM also return the
245 first occurrence of that value in the time component.
247 Example: "VDEF:avg=mydata,AVERAGE"
249 STDEV
250 Returns the standard deviation of the values.
252 Example: "VDEF:stdev=mydata,STDEV"
254 LAST, FIRST
255 Return the last/first value including its time. The time for FIRST
256 is actually the start of the corresponding interval, whereas LAST
257 returns the end of the corresponding interval.
259 Example: "VDEF:first=mydata,FIRST"
261 TOTAL
262 Returns the rate from each defined time slot multiplied with the
263 step size. This can, for instance, return total bytes transfered
264 when you have logged bytes per second. The time component returns
265 the number of seconds.
267 Example: "VDEF:total=mydata,TOTAL"
269 PERCENT
270 This should follow a D\bDE\bEF\bF or C\bCD\bDE\bEF\bF _\bv_\bn_\ba_\bm_\be. The _\bv_\bn_\ba_\bm_\be is popped,
271 another number is popped which is a certain percentage (0..100).
272 The data set is then sorted and the value returned is chosen such
278 numbers. (NaN < -INF < finite values < INF)
280 Example: "VDEF:perc95=mydata,95,PERCENT"
282 LSLSLOPE, LSLINT, LSLCORREL
283 Return the parameters for a L\bLeast S\bSquares L\bLine _\b(_\by _\b= _\bm_\bx _\b+_\bb_\b) which
285 line related to the COUNT position of the data. LSLINT is the
287 the graph. LSLCORREL is the Correlation Coefficient (also know as
288 Pearson's Product Moment Correlation Coefficient). It will range
289 from 0 to +/-1 and represents the quality of fit for the approxima-
290 tion.
292 Example: "VDEF:slope=mydata,LSLSLOPE"
295 rrdgraph gives an overview of how r\brr\brd\bdt\bto\boo\bol\bl g\bgr\bra\bap\bph\bh works. rrdgraph_data
296 describes D\bDE\bEF\bF,C\bCD\bDE\bEF\bF and V\bVD\bDE\bEF\bF in detail. rrdgraph_rpn describes the R\bRP\bPN\bN
298 all of the graph and print functions.
300 Make sure to read rrdgraph_examples for tips&tricks.
303 Program by Tobias Oetiker <tobi@oetiker.ch>
305 This manual page by Alex van den Bogaerdt <alex@ergens.op.het.net>
309 1.3.0 2008-03-15 RRDGRAPH_RPN(1)