X-Git-Url: https://git.octo.it/?p=rrdtool.git;a=blobdiff_plain;f=doc%2Frrdgraph_rpn.pod;h=5558c224b70c8e15bb3455911ebeb77158695abe;hp=16c5996c4de33405d6317ade27eee328529f105f;hb=3b8e10c66bfeb447e8b06b7296f748c405c8453d;hpb=4b4a568a4322288a7ec2e4b63e4596f76d65b76f diff --git a/doc/rrdgraph_rpn.pod b/doc/rrdgraph_rpn.pod index 16c5996..5558c22 100644 --- a/doc/rrdgraph_rpn.pod +++ b/doc/rrdgraph_rpn.pod @@ -1,41 +1,37 @@ =head1 NAME -rrdtool graph - Round Robin Database tool grapher functions +rrdgraph_rpn - About RPN Math in rrdtool graph -WARNING: This is for version 1.1.x which is B> software. -The software may contain serious bugs. Some of the items -described in here may not yet exist (although this should -be mentioned) or still be in the alpha stage. As with every -other RRDtool release: use at your own risk. In contrast with -the stable version of RRDtool, this release may contain bugs -known to the authors. It is highly recommended that you subscribe -to the mailing list. +=head1 SYNOPSIS -=head1 SYNOPSYS - -IRPN expressionE> := -IvnameE>|IoperatorE>|IvalueE> -[ , IRPN expressionE>] +I:=I|I|I[,I] =head1 DESCRIPTION If you have ever used a traditional HP calculator you already know -B. The idea behind B is that you have a stack and push +B (Reverse Polish Notation). +The idea behind B is that you have a stack and push your data onto this stack. Whenever you execute an operation, it takes as many elements from the stack as needed. Pushing is done -implicit so whenever you specify a number or a variable, it gets -pushed automatically. +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. For B instructions, the stack is processed for each +data point on the graph. B instructions work on an entire data set in +one run. Note, that currently B instructions only support a limited +list of functions. + +Example: C -At the end of the calculation there should be one and exactly one -value left on the stack. This is the outcome of the function and -this is what is put into the I. For B instructions, -the stack is processed for each data point on the graph. B -instructions work on an entire data set in one run. +This will set variable "maximum" which you now can use in the rest +of your RRD script. Example: C This means: push variable I, 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. As you may have guessed, this instruction means nothing more than I. The real power of B lies in the @@ -43,7 +39,7 @@ fact that it is always clear in which order to process the input. For expressions like C you need to multiply 3 with 5 first before you add I to get I. However, with parentheses you could change this order: C. In B, you -would do C and need no parentheses. +would do C without the need for parentheses. =head1 OPERATORS @@ -53,27 +49,22 @@ would do C and need no parentheses. B -I - Pop two elements from the stack, compare them for the selected condition and return 1 for true or 0 for false. Comparing an I or an -I value will always result in 0 (false). +I value will result in I returned ... which will also be +treated as false by the B call. B -I - Pop one element from the stack, compare this to I respectively to I. Returns 1 for true or 0 for false. B -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 +Pops three elements from the stack. If the element popped last is 0 +(false), the value popped first is pushed back onto the stack, +otherwise the value popped second is pushed back. This does, indeed, +mean that any value other than 0 is considered to be true. Example: C should be read as C @@ -81,11 +72,12 @@ Z<> =item Comparing values -B +B -Pops two elements from the stack and returns the lesser or larger. -The two numbers shouldn't be I or I, if they are -that value is pushed back onto the stack as the result. +Pops two elements from the stack and returns the smaller or larger, +respectively. Note that I is larger than anything else. +If one of the input numbers is I then the result of the operation will be +I too. B @@ -109,15 +101,163 @@ B<+, -, *, /, %> Add, subtract, multiply, divide, modulo -B +B + +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 + +Sine and cosine (input in radians), log and exp (natural logarithm), +square root. + +B + +Arctangent (output in radians). -Sine, cosine (input in radians), log, exp (natural logarithm) +B + +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 will convert C +components into an angle in degrees. B -Round down,up to the nearest integer +Round down or up to the nearest integer. -Z<> +B + +Convert angle in degrees to radians, or radians to degrees. + +B + +Take the absolute value. + +=item Set Operations + +B + +Pop one element from the stack. This is the I of items to be sorted +(or reversed). The top I of the remaining elements are then sorted +(or reversed) in place on the stack. + +Example: C will +compute the average of the values v1 to v6 after removing the smallest and +largest. + +B + +Pop one element (I) from the stack. Now pop I elements and build the +average, ignoring all UNKNOWN values in the process. + +Example: C + +B + +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) + +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. + +B + +Create a "sliding window" average/sigma of another data series, that also +shifts the data series by given amounts of of time as well + +Usage - explicit stating shifts: +CDEF:predict=,...,,n,,x,PREDICT +CDEF:sigma=,...,,n,,x,PREDICTSIGMA + +Usage - shifts defined as a base shift and a number of time this is applied +CDEF:predict=,-n,,x,PREDICT +CDEF:sigma=,-n,,x,PREDICTSIGMA + +Example: +CDEF:predict=172800,86400,2,1800,x,PREDICT + +This will create a half-hour (1800 second) sliding window average/sigma of x, that +average is essentially computed as shown here: + + +---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---> + now + shift 1 t0 + <-----------------------> + window + <---------------> + shift 2 + <-----------------------------------------------> + window + <---------------> + shift 1 t1 + <-----------------------> + window + <---------------> + shift 2 + <-----------------------------------------------> + window + <---------------> + + Value at sample (t0) will be the average between (t0-shift1-window) and (t0-shift1) + and between (t0-shift2-window) and (t0-shift2) + Value at sample (t1) will be the average between (t1-shift1-window) and (t1-shift1) + and between (t1-shift2-window) and (t1-shift2) + + +The function is by design NAN-safe. +This also allows for extrapolation into the future (say a few days) +- you may need to define the data series whit the optional start= parameter, so that +the source data series has enough data to provide prediction also at the beginning of a graph... + +Here an example, that will create a 10 day graph that also shows the +prediction 3 days into the future with its uncertainty value (as defined by avg+-4*sigma) +This also shows if the prediction is exceeded at a certain point. + +rrdtool graph image.png --imgformat=PNG \ + --start=-7days --end=+3days --width=1000 --height=200 --alt-autoscale-max \ + DEF:value=value.rrd:value:AVERAGE:start=-14days \ + LINE1:value#ff0000:value \ + CDEF:predict=86400,-7,1800,value,PREDICT \ + CDEF:sigma=86400,-7,1800,value,PREDICTSIGMA \ + CDEF:upper=predict,sigma,3,*,+ \ + CDEF:lower=predict,sigma,3,*,- \ + LINE1:predict#00ff00:prediction \ + LINE1:upper#0000ff:upper\ certainty\ limit \ + LINE1:lower#0000ff:lower\ certainty\ limit \ + CDEF:exceeds=value,UN,0,value,lower,upper,LIMIT,UN,IF \ + TICK:exceeds#aa000080:1 + +Note: Experience has shown that a factor between 3 and 5 to scale sigma is a good +discriminator to detect abnormal behavior. This obviously depends also on the type +of data and how "noisy" the data series is. + +This prediction can only be used for short term extrapolations - say a few days into the future- =item Special values @@ -138,47 +278,39 @@ set or otherwise the result of this B at the previous time step. This allows you to do calculations across the data. This function cannot be used in B instructions. -Z<> - -=item Time +B -Time inside RRDtool is measured in seconds since the epoch. This -epoch is defined to be S>. +Pushes an I value if this is the first value of a data +set or otherwise the result of the vname variable at the previous time +step. This allows you to do calculations across the data. This +function cannot be used in B instructions. -Z<> +B -=over 4 +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 instructions. -=item NOW +=item Time -Pushes the current time on the stack. +Time inside RRDtool is measured in seconds since the epoch. The +epoch is defined to be S>. -Z<> +B -=item TIME +Pushes the current time on the stack. -Pushes the time the currently processed value was taken onto the stack. +B