Introduction

The -rpn option runs a reverse polish notation (rpn) calculator. The option is preliminary and the mode of operation may change.

The calculator includes 10 registers that are persistant. The stack is initialized with each grib message. (The grid values are put on the top of the stack.) The registers are initialized when wgrib2 is started. Consequently the registers allow you to save data between different grib messages.

Uses

• change of units when importing data (gribifying data)
• computations: ex, U,V -> wind speed, wind direction, potential temperature
• merging data
• complex masking of data
• changing units before writing text/ieee files
• removing extreme data values

Usage

-rpn  A:B:C:...
    A,B,C,.. = number or an operator, function or number

Operators and Functions:

  +, -, *, / 
  <, <=, ==, !=, >=, >
  sin, cos, tan
  abs
  sq, x*x
  sqrt, square root
  1/x
  floor
  max, the maximum value of the top and top-1
  min, the minimum value of the top and top-1
  merge, top of the stack unless it is undefined then the top-1
  mask
  yrev, for nx-ny grids,  we:sn -> we:ns

  clr, clear the stack
  dup, duplicate the top of the stack
  pop, remove the top of the stack
  exc, exchange the top 2 stack entries
  pi, put pi on top of stack

  clr_I, clear register I,  I=0,1..,9  
  rcl_I, push register I on top of stack,  I=0,1..,9  
  sto_I, save top of stack in register I,  I=0,1..,9  
  rcl_lat, push latitudes onto the top of the stack
  rcl_lon, push longitudes onto the top of the stack

 print_corr, write cosine weighted spatial correlation
 print_max, print_min
 print_rms, write cosine weighted RMS

Examples

The standard units of grib temperature is K but you want the output to be in Celcius.

$ wgrib2 a.grb -match ":TMP:850 mb:" -rpn 273.15:- -text C.dat

Fahrenheit is easy too (F = (K-273.15)*9/5+32).

$ wgrib2 a.grb -match ":TMP:850 mb:" -rpn "273.15:-:9:*:5:/:32:+" -text C.dat

Suppose someone made a mistake and the latent heat flux (LHTFL) had the wrong sign. RPN to the rescue.

$ wgrib2 a.grb -match ":LHTFL:" -rpn "-1:*" -grib_out new_lhtfl.grb

$ wgrib2 a.grb -if ":LHTFL:" -rpn "-1:*" -fi -grib_out new.grb

$ wgrib2 a.grb -if ":(LHTFL|SHTFL):" -rpn "-1:*" -fi -grib_out new.grb

print_corr write cosine weighted spatial correlation R(TOP-1), R(TOP)
print_max write max(R(TOP)) to stdout
print_min write min(R(TOP)) to stdout
print_rms write cosine weighted RMS(R(TOP-1)-R(TOP))

See also: