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 Sine and cosine (input in radians), log and exp (natural loga-
100 rithm), square root.
104 Arctangent (output in radians).
108 Arctangent of y,x components (output in radians). This pops one
109 element from the stack, the x (cosine) component, and then a sec-
110 ond, which is the y (sine) component. It then pushes the arctan-
111 gent of their ratio, resolving the ambiguity between quadrants.
113 Example: "CDEF:angle=Y,X,ATAN2,RAD2DEG" will convert "X,Y" compo-
114 nents into an angle in degrees.
118 Round down or up to the nearest integer.
122 Convert angle in degrees to radians, or radians to degrees.
126 Take the absolute value.
128 Set Operations
133 then sorted (or reversed) in place on the stack.
135 Example: "CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/"
136 will compute the average of the values v1 to v6 after removing the
137 smallest and largest.
141 Pop one element (_\bc_\bo_\bu_\bn_\bt) from the stack. Now pop _\bc_\bo_\bu_\bn_\bt elements and
142 build the average, ignoring all UNKNOWN values in the process.
144 Example: "CDEF:x=a,b,c,d,4,AVG"
148 Create a "sliding window" average of another data series.
150 Usage: CDEF:smoothed=x,1800,TREND
152 This will create a half-hour (1800 second) sliding window average
153 of x. The average is essentially computed as shown here:
155 +---!---!---!---!---!---!---!---!--->
156 now
157 delay t0
158 <--------------->
159 delay t1
160 <--------------->
161 delay t2
162 <--------------->
164 Value at sample (t0) will be the average between (t0-delay) and (t0)
165 Value at sample (t1) will be the average between (t1-delay) and (t1)
166 Value at sample (t2) will be the average between (t2-delay) and (t2)
168 Special values
171 Pushes an unknown value on the stack
175 Pushes a positive or negative infinite value on the stack. When
176 such a value is graphed, it appears at the top or bottom of the
177 graph, no matter what the actual value on the y-axis is.
183 allows you to do calculations across the data. This function can-
189 otherwise the result of the vname variable at the previous time
190 step. This allows you to do calculations across the data. This
195 Pushes the number 1 if this is the first value of the data set, the
196 number 2 if it is the second, and so on. This special value allows
197 you to make calculations based on the position of the value within
200 Time
201 Time inside RRDtool is measured in seconds since the epoch. The
202 epoch is defined to be "Thu Jan 1 00:00:00 UTC 1970".
206 Pushes the current time on the stack.
210 Pushes the time the currently processed value was taken at onto the
211 stack.
216 valid at that time including daylight saving time if your OS sup-
217 ports it, and pushes the result on the stack. There is an elabo-
218 rate example in the examples section below on how to use this.
220 Processing the stack directly
223 Duplicate the top element, remove the top element, exchange the two
224 top elements.
232 MAXIMUM, MINIMUM, AVERAGE
233 Return the corresponding value, MAXIMUM and MINIMUM also return the
234 first occurrence of that value in the time component.
236 Example: "VDEF:avg=mydata,AVERAGE"
238 LAST, FIRST
239 Return the last/first value including its time. The time for FIRST
240 is actually the start of the corresponding interval, whereas LAST
241 returns the end of the corresponding interval.
243 Example: "VDEF:first=mydata,FIRST"
245 TOTAL
246 Returns the rate from each defined time slot multiplied with the
247 step size. This can, for instance, return total bytes transfered
248 when you have logged bytes per second. The time component returns
249 the number of seconds.
251 Example: "VDEF:total=mydata,TOTAL"
253 PERCENT
254 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,
255 another number is popped which is a certain percentage (0..100).
256 The data set is then sorted and the value returned is chosen such
262 numbers. (NaN < -INF < finite values < INF)
264 Example: "VDEF:perc95=mydata,95,PERCENT"
266 LSLSLOPE, LSLINT, LSLCORREL
267 Return the parameters for a L\bLeast S\bSquares L\bLine _\b(_\by _\b= _\bm_\bx _\b+_\bb_\b) which
269 line related to the COUNT position of the data. LSLINT is the
271 the graph. LSLCORREL is the Correlation Coefficient (also know as
272 Pearson's Product Moment Correlation Coefficient). It will range
273 from 0 to +/-1 and represents the quality of fit for the approxima-
274 tion.
276 Example: "VDEF:slope=mydata,LSLSLOPE"
279 rrdgraph gives an overview of how r\brr\brd\bdt\bto\boo\bol\bl g\bgr\bra\bap\bph\bh works. rrdgraph_data
280 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
282 all of the graph and print functions.
284 Make sure to read rrdgraph_examples for tips&tricks.
287 Program by Tobias Oetiker <tobi@oetiker.ch>
289 This manual page by Alex van den Bogaerdt <alex@ergens.op.het.net>
293 1.2.26 2007-11-20 RRDGRAPH_RPN(1)