Ch7 Sec11.

SPECIAL SYMBOLS

PPLUS defines a number of global symbols which are available to the user. They are documented in the chapter "Customizing Plots", section PPLUS special symbols and also listed in the  PPLUS Users Guide.

There are a few symbols, generated automatically by plots or at Ferret run-time, which are not documented in the PLOT PLUS for Ferret Users Guide. Those are shown like all symbols by SHOW SYMBOLS, and their values can be used in scripts, but they cannot be directly redefined by the user.

PPL$XPIXEL
PPL$YPIXEL

the number of pixels in the horizontal (X) and vertical (Y) size of the current Ferret output window. Note: these are "0" if there is no current window -- hence they can be used as a test of whether there is an open window.

BYTEORDER

gives "BIG" or "LITTLE" according to endianness of the CPU

FERRET_MEMORY

give the current memory setting (Mwords).

FERRET_VERSION

give the Ferret version that is running.

FERRET_PLATFORM

give the Ferret version and the platform Ferret is running on.

SESSION_DATE
SESSION_TIME

gives the date and time when the current session began.

CURRENT_DATE
CURRENT_TIME

gives the date and time when the given symbol is evaluated.  Resets each time you SHOW SYMBOL CURRENT_DATE (or CURRENT_TIME)  or evaluate one of them e.g.  SAY ($CURRENT_TIME).

CLOCK_SECS

gives the elapsed time in seconds since the start of the Ferret session.  This is done via a call  to the intrinsic function SYSTEM_CLOCK and therefore its results may be system dependent. 

When it is evaluated, this calls the intrinsic function Dtime and sets the value to the delta-CPU-time  since the last evaluation of this symbol (with SHOW SYMBOL, or with an evaluation of ($DELTA_CPU) ). It is called and set to zero Ferret initializes, so the first evaluation gets delta-cpu time since the start of the Ferret session.

FER_LAST_ERROR

if defined, contains the error string associated with the last Ferret error that was encountered. If it was a multi-line string, the lines are concatenated together.

LAST_GO_FILE

if defined, contains the name, including the path, of the last GO script that was executed.

Examples using the clock and timing symbols.

>ferret
 	NOAA/PMEL TMAP
 	FERRET v6.2  
 	Linux(g77) 2.4.21-32 - 05/06/09
 	14-May-09 15:44     

yes? show symbols  ! several symbols are set at startup.
...
FERRET_VERSION = "6.2"
FERRET_PLATFORM = "Linux(g77) 2.4.21-32"
SESSION_DATE = "14-May-09"
SESSION_TIME = "15:44"
DELTA_CPU = "0.01"
CLOCK_SECS = "2.62"
CURRENT_DATE = "14-May-09"
CURRENT_TIME = "15:52:17"
FERRET_MEMORY = "25.6"

yes? USE mydata.nc
yes? SHADE/K=1 temp[L=@ave]
yes? SHOW SYM DELTA_CPU, CLOCK_SECS
DELTA_CPU = "0.18"
CLOCK_SECS = "2.89"

yes? REPEAT/K=1:10 shade temp[L=@ave]

! DELTA_CPU since the evaluation just above on the SHOW SYM.
yes? LET time_ten_plots = ($DELTA_CPU)  
 !-> DEFINE VARIABLE time_ten_plots = 0.88

! This command evaluates the CPU time since the last 
! evaluation, which was just above.

yes? sh sym DELTA_CPU
DELTA_CPU = "0"

! To get elapsed time for a particular piece of calculation,
! set a variable or symbol containing one evaluation of CLOCK_SECS
! and subtract that from a later evaluation of CLOCK_SECS.

yes? let secs_0 = ($clock_secs)

yes? repeat/k=1:10 (shade/pal=rnb2 temp[L=@max])
yes? let elapsed_clock_time = `($clock_secs) - secs_0`

! SESSION_DATE and SESSION_TIME are fixed for the entire session,
! CURRENT_DATE and CURRENT_TIME update when they are evaluated.
yes? SH SYM session_date, current_date, session_time, current_time
SESSION_DATE = "14-May-09"
SESSION_TIME = "15:52"
CURRENT_DATE = "14-May-09"
CURRENT_DATE = "15:52:20"