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 stack and push your data onto this stack. Whenever you execute an
15 operation, it takes as many elements from the stack as needed. Pushing
16 is done implicitly, so whenever you specify a number or a variable, it
17 gets pushed onto the stack automatically.
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 only 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 operator _\b*. The operator needs two elements and uses those to return
35 one value. This value is then stored in _\bm_\by_\bd_\ba_\bt_\ba_\bb_\bi_\bt_\bs. As you may have
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
48 condition and return 1 for true or 0 for false. Comparing an
49 _\bu_\bn_\bk_\bn_\bo_\bw_\bn or an _\bi_\bn_\bf_\bi_\bn_\bi_\bt_\be value will always result in 0 (false).
54 respectively 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
55 or 0 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
106 logarithm), 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
116 second, which is the y (sine) component. It then pushes the
117 arctangent of their ratio, resolving the ambiguity between
118 quadrants.
120 Example: "CDEF:angle=Y,X,ATAN2,RAD2DEG" will convert "X,Y"
121 components into an angle in degrees.
125 Round down or up to the nearest integer.
129 Convert angle in degrees to radians, or radians to degrees.
133 Take the absolute value.
135 Set Operations
140 then sorted (or reversed) in place on the stack.
142 Example: "CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/"
143 will compute the average of the values v1 to v6 after removing the
144 smallest and largest.
148 Pop one element (_\bc_\bo_\bu_\bn_\bt) from the stack. Now pop _\bc_\bo_\bu_\bn_\bt elements and
149 build the average, ignoring all UNKNOWN values in the process.
151 Example: "CDEF:x=a,b,c,d,4,AVG"
155 Create a "sliding window" average of another data series.
157 Usage: CDEF:smoothed=x,1800,TREND
159 This will create a half-hour (1800 second) sliding window average
160 of x. The average is essentially computed as shown here:
162 +---!---!---!---!---!---!---!---!--->
163 now
164 delay t0
165 <--------------->
166 delay t1
167 <--------------->
168 delay t2
169 <--------------->
172 Value at sample (t0) will be the average between (t0-delay) and (t0)
173 Value at sample (t1) will be the average between (t1-delay) and (t1)
174 Value at sample (t2) will be the average between (t2-delay) and (t2)
176 TRENDNAN is - in contrast to TREND - NAN-safe. If you use TREND and
177 one source value is NAN the complete sliding window is affected.
178 The TRENDNAN operation ignores all NAN-values in a sliding window
179 and computes the average of the remaining values.
181 Special values
184 Pushes an unknown value on the stack
188 Pushes a positive or negative infinite value on the stack. When
189 such a value is graphed, it appears at the top or bottom of the
190 graph, no matter what the actual value on the y-axis is.
196 allows you to do calculations across the data. This function
202 otherwise the result of the vname variable at the previous time
203 step. This allows you to do calculations across the data. This
208 Pushes the number 1 if this is the first value of the data set, the
209 number 2 if it is the second, and so on. This special value allows
210 you to make calculations based on the position of the value within
213 Time
214 Time inside RRDtool is measured in seconds since the epoch. The
215 epoch is defined to be "Thu Jan 1 00:00:00 UTC 1970".
219 Pushes the current time on the stack.
223 Pushes the time the currently processed value was taken at onto the
224 stack.
229 valid at that time including daylight saving time if your OS
230 supports it, and pushes the result on the stack. There is an
231 elaborate example in the examples section below on how to use this.
233 Processing the stack directly
236 Duplicate the top element, remove the top element, exchange the two
237 top elements.
245 MAXIMUM, MINIMUM, AVERAGE
246 Return the corresponding value, MAXIMUM and MINIMUM also return the
247 first occurrence of that value in the time component.
249 Example: "VDEF:avg=mydata,AVERAGE"
251 STDEV
252 Returns the standard deviation of the values.
254 Example: "VDEF:stdev=mydata,STDEV"
256 LAST, FIRST
257 Return the last/first value including its time. The time for FIRST
258 is actually the start of the corresponding interval, whereas LAST
259 returns the end of the corresponding interval.
261 Example: "VDEF:first=mydata,FIRST"
263 TOTAL
264 Returns the rate from each defined time slot multiplied with the
265 step size. This can, for instance, return total bytes transfered
266 when you have logged bytes per second. The time component returns
267 the number of seconds.
269 Example: "VDEF:total=mydata,TOTAL"
271 PERCENT
272 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,
273 another number is popped which is a certain percentage (0..100).
274 The data set is then sorted and the value returned is chosen such
280 numbers. (NaN < -INF < finite values < INF)
282 Example: "VDEF:perc95=mydata,95,PERCENT"
284 LSLSLOPE, LSLINT, LSLCORREL
285 Return the parameters for a L\bLeast S\bSquares L\bLine _\b(_\by _\b= _\bm_\bx _\b+_\bb_\b) which
287 line related to the COUNT position of the data. LSLINT is the
289 the graph. LSLCORREL is the Correlation Coefficient (also know as
290 Pearson's Product Moment Correlation Coefficient). It will range
291 from 0 to +/-1 and represents the quality of fit for the
292 approximation.
294 Example: "VDEF:slope=mydata,LSLSLOPE"
297 rrdgraph gives an overview of how r\brr\brd\bdt\bto\boo\bol\bl g\bgr\bra\bap\bph\bh works. rrdgraph_data
298 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
300 all of the graph and print functions.
302 Make sure to read rrdgraph_examples for tips&tricks.
305 Program by Tobias Oetiker <tobi@oetiker.ch>
307 This manual page by Alex van den Bogaerdt <alex@vandenbogaerdt.nl> with
308 corrections and/or additions by several people
312 1.3.8 2009-02-21 RRDGRAPH_RPN(1)