other:python:misc_by_jyp
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other:python:misc_by_jyp [2023/05/04 12:33] jypeter [Base notions] Improved |
other:python:misc_by_jyp [2023/05/04 15:25] jypeter [Numerical values] Lots of changes |
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| ==== Numerical values ==== | ==== Numerical values ==== | ||
| - | * Binary data representation of some numbers (not everythin is listed here): | + | * Binary data representation of some numbers (only some common types are listed here): |
| + | * Languages and packages **references** used below: | ||
| + | * Python: [[https://numpy.org/doc/stable/reference/arrays.scalars.html#sized-aliases|NumPy Sized aliases]] | ||
| + | * NetCDF: [[https://docs.unidata.ucar.edu/nug/current/md_types.html|Data Types]], [[https://docs.unidata.ucar.edu/netcdf-fortran/current/f90-variables.html#f90-language-types-corresponding-to-netcdf-external-data-types|Fortran related Data Types]], [[https://docs.unidata.ucar.edu/nug/current/_c_d_l.html#cdl_data_types|CDL Data Types]] | ||
| + | * Fortran: Intel Fortran Compiler [[https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2023-1/intrinsic-data-types.html|Intrinsic Data Types]] | ||
| * [[https://en.wikipedia.org/wiki/Integer_(computer_science)|Integers]] | * [[https://en.wikipedia.org/wiki/Integer_(computer_science)|Integers]] | ||
| * Range: | * Range: | ||
| - | * 4-byte integers: −2,147,483,648 to 2,147,483,647 | + | * 4-byte //signed// integers: ''−2,147,483,648'' to ''2,147,483,647'' |
| * Python: ''numpy.int32'' | * Python: ''numpy.int32'' | ||
| - | * [[https://docs.unidata.ucar.edu/nug/current/md_types.html|NetCDF]], [[https://docs.unidata.ucar.edu/netcdf-fortran/current/f90-variables.html#f90-language-types-corresponding-to-netcdf-external-data-types|NetCDF-Fortran]]: ''int'', ''NC_INT64'', ''NF90_INT'' | + | * NetCDF: ''int'', ''NC_INT'' or ''NC_LONG'', ''NF90_INT'' |
| - | * Fortran: | + | * Fortran: ''INTEGER*4'' |
| - | * 8-byte integers: −9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 | + | * 8-byte //signed// integers: ''−9,223,372,036,854,775,808'' to ''9,223,372,036,854,775,807'' |
| * Python: ''numpy.int64'' | * Python: ''numpy.int64'' | ||
| - | * [[https://docs.unidata.ucar.edu/nug/current/md_types.html|NetCDF]]: ''int64'', ''NC_INT64'' | + | * NetCDF: ''int64'', ''NC_INT64'' |
| - | * Fortran: | + | * Fortran: ''INTEGER*8'' |
| * Tech note: signed integers use [[https://en.wikipedia.org/wiki/Two%27s_complement|two's complement]] for coding negative integers | * Tech note: signed integers use [[https://en.wikipedia.org/wiki/Two%27s_complement|two's complement]] for coding negative integers | ||
| * [[https://en.wikipedia.org/wiki/IEEE_754|Floating point numbers]] (//IEEE 754// standard aka //IEEE Standard for Binary Floating-Point for Arithmetic//) | * [[https://en.wikipedia.org/wiki/IEEE_754|Floating point numbers]] (//IEEE 754// standard aka //IEEE Standard for Binary Floating-Point for Arithmetic//) | ||
| * Range: | * Range: | ||
| - | * 4-byte float: ~8 significant digits * 10E±38 | + | * 4-byte float: ''~8 significant digits * 10E±38'' |
| * Python: ''numpy.float32'' | * Python: ''numpy.float32'' | ||
| - | * [[https://docs.unidata.ucar.edu/nug/current/md_types.html|NetCDF]], [[https://docs.unidata.ucar.edu/netcdf-fortran/current/f90-variables.html#f90-language-types-corresponding-to-netcdf-external-data-types|NetCDF-Fortran]]: | + | * NetCDF: ''float'', ''NC-FLOAT'', ''NF90_FLOAT'' |
| - | * Fortran: | + | * Fortran:''REAL*4'' |
| * See also [[https://en.wikipedia.org/wiki/Single-precision_floating-point_format|Single-precision floating-point format]] | * See also [[https://en.wikipedia.org/wiki/Single-precision_floating-point_format|Single-precision floating-point format]] | ||
| - | * 8-byte float: ~15 significant digits * 10E±308 | + | * 8-byte float: ''~15 significant digits * 10E±308'' |
| * Python: ''numpy.float64'' | * Python: ''numpy.float64'' | ||
| - | * [[https://docs.unidata.ucar.edu/nug/current/md_types.html|NetCDF]], [[https://docs.unidata.ucar.edu/netcdf-fortran/current/f90-variables.html#f90-language-types-corresponding-to-netcdf-external-data-types|NetCDF-Fortran]]: | + | * NetCDF: ''double'', ''NC_DOUBLE'', ''NF90_DOUBLE'' |
| - | * Fortran: | + | * Fortran: ''REAL*8'' |
| - | * Special values: | + | * **Special values**: |
| - | * [[https://en.wikipedia.org/wiki/NaN|NaN]] (''numpy.nan''): //Not a Number// | + | * [[https://en.wikipedia.org/wiki/NaN|NaN]]: //Not a Number// |
| - | * Infinity (''-numpy.inf'' and ''numpy.inf'') | + | * Python: ''numpy.nan'' |
| + | * Infinity | ||
| + | * Python: ''-numpy.inf'' and ''numpy.inf'' | ||
| * Note: it is cleaner to use masks (and [[https://numpy.org/doc/stable/reference/maskedarray.generic.html|Numpy masked arrays]]) than NaNs, when you have to deal with missing values ! | * Note: it is cleaner to use masks (and [[https://numpy.org/doc/stable/reference/maskedarray.generic.html|Numpy masked arrays]]) than NaNs, when you have to deal with missing values ! | ||
| - | * [[https://en.wikipedia.org/wiki/Bit_numbering|Bit numbering]] | + | * <wrap hi>The RISKS of working with (the wrong) floats</wrap>: |
| - | * [[https://en.wikipedia.org/wiki/Endianness|Endianness]] | + | * [[https://en.wikipedia.org/wiki/Round-off_error|Round-off error]] |
| + | * [[https://en.wikipedia.org/wiki/Catastrophic_cancellation|Catastrophic cancellation]] | ||
| + | * [[https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html|What Every Computer Scientist Should Know About Floating-Point Arithmetic]] | ||
| * A rather technical example: we //play// with a numpy 4-byte integer scalar | * A rather technical example: we //play// with a numpy 4-byte integer scalar | ||
| * <code>>>> one_int32 = np.int32(1) | * <code>>>> one_int32 = np.int32(1) | ||
other/python/misc_by_jyp.txt · Last modified: 2024/04/19 12:02 by jypeter
