## Retrieving data using Matlab

The EPICS Archiver Appliance support multiple MIME-types when retrieving
data and one of the supported MIME-types is the Matlab file format. The
process of getting archive data into Matlab consists of

1. Constructing a URL to the server. See
   [Constructing a data retrieval URL](./web-client.md#constructing-a-data-retrieval-url)
   for the URL format for data retrieval.
2. Using `urlwrite` to download data from this URL into a file.
3. Loading this file into Matlab.

Here\'s some sample code that is used to get the data for PV
`VPIO:IN20:111:VRAW`

```matlab
urlwrite('http://test-arch.slac.stanford.edu:17668/retrieval/data/getData.mat', ...
    'temp.mat', 'get', ...
    {'pv', 'VPIO:IN20:111:VRAW', 'from', '2012-09-27T08:00:00.000Z', 'to', '2012-09-28T08:00:00.000Z'})

dat = load('temp.mat')
delete('temp.mat')

try
    header = dat.header;
    data = dat.data;
catch
    fprintf('Could not get data from file\n');
    return
end

header
data
```

Here\'s a screenshot of this sample code being executed in a Matlab
environment.

![image](../../images/matlab1.png)

The `.mat` response contains two objects, a header and a data object.

- The header object is indexed by the string `header` and is a
  MLStructure with fields containing some provenance information.
- The data object is indexed by the string `data` and is a MLStructure
  with these fields.
  1. `epochSeconds` - contains Java epoch seconds as a 1x1 uint64
     array. The times are in UTC; so any conversion to local time
     needs to happen at the client.
  2. `values` - contains the values for the samples. All scalars come
     as a 1x1 double array. Waveforms come as a 1x*elementcount*
     double array where _elementcount_ is the EPICS element count of
     the waveform.
  3. `nanos` - contains the nano second value of the EPICS record
     processing timestamp as a 1x1 uint64 array. Some installations
     embed the beam code/pulse id into this field.
  4. `isDST` - contains booleans that indicate if the time indicated
     by `epochSeconds` was in daylight savings time in the timezone
     of the server.