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Introduction

Workshop Overview. Labs important: you must invest the time

arleen
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Introduction

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    2. Workshop Overview Labs important: you must invest the time osmosis method of learning does not work

    3. NCL variable model is based on the netCDF variable model

    4. netCDF files self describing (ideally) all info contained within the file no external information needed to determine file contents portable [machine independent]

    5. Examining a netCDF file ncdump file_name | less dumps the entire contents of a file; prints every value ncdump -h file_name | less Dumps header information [most commonly used] NCL equivalent: ncl_filedump file_name | less ncdump -v U file_name | less NCL equivalent: ncl_filedump v U file_name | less Note: ncdump is a Unidata utility not a netCDF Operator (NCO / CDO) not associated with NCL

    6. Parts of netCDF file

    7. netCDF/NCL variable array [could be of length 1 (scalar)] (may) have additional information

    8. visual: simple 2D netCDF Variable coordinate variables (rectilinear grid)

    9. netCDF [NCL] Variable model

    10. Detailed Look netCDF Variable (NCL)

    11. Why Know NCL/netCDF Variable Model

    12. Integrated processing environment

    13. NCL Support Documentation and Examples http://www.ncl.ucar.edu/ numerous downloadable examples to get you going downloadable reference manuals [pdf], FAQ

    14. NCAR Command Language Complete Programming Language data types variables operators expressions conditional statements loops functions/procedures/graphics

    15. Running NCL Interactive Mode (Command line) ncl [options][command-line-arguments] <return> ncl> enter commands ncl> quit <return> can save interactive commands ncl> record file_name ncl> stop record

    16. NCL predefined options ncl hnxV [predfined options are preceded by dash] may be used for interactive or batch mode informational ncl h [display predefined options and usage and exit] ncl V [print the NCL version and exit] action ncl x [echo statements as encountered (debug)] ncl n [don't enumerate dimensions of values in print() ] multiple predefined options ncl nx [ not ncl n x ]

    17. Sample Batch Script: sample.ncl

    20. Outline: NCL Language Basics special syntax characters data types Variables ? netCDF/NCL variable model attributes _FillValue named dimensions coordinate variables print and printVarSummary shaping subscripting

    21. NCL Syntax Characters

    22. Data Types Numeric double (64 bit) float (32 bit) long (32 or 64 bit) integer (32 bit) short (16 bit) byte ( 8 bit, 0-255) complex NOT supported non-Numeric string character graphic file logical list

    23. Simple Variable Assignment

    24. Conversion between data types NCL is a strongly typed language coercion implicit conversion of one type to another automatic coercion when no info is lost let i be integer and x be float or double fortran: x=i and i=x NCL: x=i and i=toint(x) many functions to perform conversions

    25. Attributes

    26. _FillValue Unidata and NCL reserved attribute most NCL functions ignore _FillValue

    27. Interactive: Variable_1

    28. Arrays

    29. NCL (netCDF) Dimensions

    30. NCL (netCDF) Coordinate Variables data coordinates [ eg: time, level, lat, lon ] strict netCDF definition 1D numeric array monotonically in[de]creasing numeric values can only be assigned to a named dimension 1D array must be the same size as dimension should not have _FillValue attribute coordinate values assigned via & character T&lat = latitude

    31. Create and Assign Coordinate Variables

    32. Access/Change/Create/Delete Meta Data

    33. netCDF [NCL] Variable model

    34. Variable Assignment

    35. Interactive: Variable_2

    36. Variable Reshaping/Reordering

    37. Variable Subscripting (1 of 3) Standard Array Subscripting ranges: start/end and [optional] stride indices separated by : omitting start/end index implies default begin/end

    38. Variable Subscripting (2 of 3) Coordinate Variable Subscripting only applies to coordinate variables same rules apply for ranges, strides, defaults use curly brackets {} standard and coordinate subs can be mixed [if no reorder]

    39. Variable Subscripting (3 of 3) Named Dimensions only used for dimension reordering indicated by | dim names must be used for each subscript named/coordinate subscripting can be mixed

    40. Standard and Coordinate Subscripting

    41. Interactive: Variable_3

    42. printing

    43. printVarSummary Print out variable (data object) information type dimension information coordinate information (if present) attributes (if present) printVarSummary (u)

    44. print (1 of 3)

    45. print (2 of 3)

    46. print (3 of 3)

    47. write_matrix(x[*][*], fmt, opt)

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