# MATLAB interface

The Matrix Laboratory (MATLAB) interface consists of a series of M-files that provide the harp_import, harp_export and harp_version functions.

Products are represented in MATLAB as structures which can be manipulated freely from within MATLAB. A product structure contains an array field for each variable contained in the product.

Products can be exported as HARP compliant products in any of the file formats supported by the HARP C library (netCDF/HDF4/HDF5). Such exported products can subsequently be processed further using the HARP command line tools.

## Dimension types

The HARP C library defines several dimension types (time, vertical, latitude etc.). This information is stored in the dimension_type field of each variable in MATLAB. If a variable is a scalar (which has no dimensions), the dimension_type field is not present.

## Data types

The HARP MATLAB interface takes care of the conversion of product and variables from the C domain to the MATLAB domain and back. This section describes the relation between types in the C domain and types in the MATLAB domain.

The table below shows the type map that is used when importing or ingesting a product, i.e. when translating from the C domain to the MATLAB domain.

Variable data arrays are converted to arrays in the product structure. The data type used for the converted array is determined from the HARP data type of the variable according to the type map shown below. Zero-dimensional arrays of length 1 are converted to MATLAB arrays of 1x1. The resulting MATLAB type is also shown in the type map.

HARP data type | MATLAB type
--- | ---
harp_type_int8 | int8
harp_type_int16 | int16
harp_type_int32 | int32
harp_type_float | single
harp_type_double | double
harp_type_string | char

## Unicode

Zero-terminated C strings received from the HARP C library are always converted to arrays of mxCHAR in MATLAB which is an unicode string.

## Examples

    ; Ingest a file and convert it to a HARP product (the
    ; file that is used in this example is an ACE-FTS file).
    product1 = harp_import("ss13799.asc")

    ; Print information about the product.
    disp(product1)

    ; Print information about the variable 'temperature'.
    disp(product1.temperature)

    ; Print the contents of the variable 'temperature'.
    product1.temperature.value

    ; Export the updated product as an HDF4 file (the format must be
    ; HDF4, HDF5 or netCDF, if no format is specified netCDF is used).
    result = harp_export(product1, "ace_fts_ss13799.hdf", "hdf4")

    ; Print the result of the export.
    disp(result)

    ; Import the HDF4 file and perform an operation to exclude the variable
    ; temperature (variable name must be in uppercase).
    product2 = harp_import("ace_fts_ss13799.hdf", "exclude(TEMPERATURE)");

    ; Print information about the product.
    disp(product2)

## API reference

This section describes the functions defined by the HARP MATLAB interface.

harp_import(filename, operations='', options='')

  Import a product from a file.

  This will first try to import the file as an HDF4, HDF5, or netCDF file that complies to the HARP Data Format. If the file is not stored using the HARP format then it will try to import it using one of the available ingestion modules.

  If the filename argument is a list of filenames or a globbing (glob.glob()) pattern then the harp.import_product() function will be called on each individual file and the result of harp.concatenate() on the imported products will be returned.

  Parameters:

    - filename (str) – Filename of the product to ingest

    - operations (str) – Actions to apply as part of the import; should be specified as a semi-colon separated string of operations.

    - options (str) – Ingestion module specific options; should be specified as a semi-colon separated string of key=value pairs; only used if the file is not in HARP format.

  Returns:

    Ingested product.

harp_export(product, filename, file_format='netcdf')

  Export a HARP compliant product.

  Parameters:

    - product (str) – Product to export.

    - filename (str) – Filename of the exported product.

    - file_format (str) – File format to use; one of ‘netcdf’, ‘hdf4’, or ‘hdf5’. If no format is specified, netcdf is used.

harp_version()

  Returns the version number of HARP.