7 Prediction functions

All functions listed here are supported in:

• Trigger expressions
• Calculated items

Some general notes on function parameters:

• Function parameters are separated by a comma
• Optional function parameters (or parameter parts) are indicated by < >
• Function-specific parameters are described with each function
• /host/key and (sec|#num)<:time shift> parameters must never be quoted

Common parameters

• /host/key is a common mandatory first parameter for the functions referencing the host item history
• (sec|#num)<:time shift> is a common second parameter for the functions referencing the host item history, where:
  • sec - maximum evaluation period in seconds (time suffixes can be used), or
  • #num - maximum evaluation range in latest collected values (if preceded by a hash mark)
  • time shift (optional) allows to move the evaluation point back in time. See more details on specifying time shift.

Function details

Some general notes on function parameters:

• Function parameters are separated by a comma
• Optional function parameters (or parameter parts) are indicated by < >
• Function-specific parameters are described with each function
• /host/key and (sec|#num)<:time shift> parameters must never be quoted

forecast(/host/key,(sec|#num)<:time shift>,time,<fit>,<mode>)

The future value, max, min, delta or avg of the item.
Supported value types: Float, Integer.

Parameters:

• See common parameters;
  
• time - the forecasting horizon in seconds (time suffixes can be used); negative values are supported;
  
• fit (optional; must be double-quoted) - the function used to fit historical data. Supported fits:
  linear - linear function (default)
  polynomialN - polynomial of degree N (1 <= N <= 6)
  exponential - exponential function
  logarithmic - logarithmic function
  power - power function
  Note that polynomial1 is equivalent to linear;
• mode (optional; must be double-quoted) - the demanded output. Supported modes:
  value - value (default)
  max - maximum
  min - minimum
  delta - max-min
  avg - average
  Note that value estimates the item value at the moment now + time; max, min, delta and avg investigate the item value estimate on the interval between now and now + time.

Comments:

• If the value to return is larger than 1.7976931348623157E+308 or less than -1.7976931348623157E+308, the return value is cropped to 1.7976931348623157E+308 or -1.7976931348623157E+308 correspondingly;
• Becomes unsupported only if misused in the expression (wrong item type, invalid parameters), otherwise returns -1 in case of errors;
• See also additional information on predictive trigger functions.

Examples:

forecast(/host/key,#10,1h) #forecast the item value in one hour based on the last 10 values
       forecast(/host/key,1h,30m) #forecast the item value in 30 minutes based on the last hour data
       forecast(/host/key,1h:now-1d,12h) #forecast the item value in 12 hours based on one hour one day ago
       forecast(/host/key,1h,10m,"exponential") #forecast the item value in 10 minutes based on the last hour data and exponential function
       forecast(/host/key,1h,2h,"polynomial3","max") #forecast the maximum value the item can reach in the next two hours based on last hour data and cubic (third degree) polynomial
       forecast(/host/key,#2,-20m) #estimate the item value 20 minutes ago based on the last two values (this can be more precise than using last(), especially if the item is updated rarely, say, once an hour)

timeleft(/host/key,(sec|#num)<:time shift>,threshold,<fit>)

The time in seconds needed for an item to reach the specified threshold.
Supported value types: Float, Integer.

Parameters:

• See common parameters;
  
• threshold - the value to reach (unit suffixes can be used);
• fit (optional; must be double-quoted) - see forecast().

Comments:

• If the value to return is larger than 1.7976931348623157E+308, the return value is cropped to 1.7976931348623157E+308;
• Returns 1.7976931348623157E+308 if the threshold cannot be reached;
• Becomes unsupported only if misused in the expression (wrong item type, invalid parameters), otherwise returns -1 in case of errors;
• See also additional information on predictive trigger functions.

Examples:

timeleft(/host/key,#10,0) #the time until the item value reaches zero based on the last 10 values
       timeleft(/host/key,1h,100) #the time until the item value reaches 100 based on the last hour data
       timeleft(/host/key,1h:now-1d,100) #the time until the item value reaches 100 based on one hour one day ago
       timeleft(/host/key,1h,200,"polynomial2") #the time until the item value reaches 200 based on the last hour data and assumption that the item behaves like a quadratic (second degree) polynomial

See all supported functions.