Fixed-Point Design Exploration in Parallel

This example shows how to explore and test fixed-point designs by distributing tests across many computers in parallel. The example uses a parfor loop to test the accuracy of a QRS detector algorithm.

Using Parallel for-Loops for Design Exploration

Like a standard for-loop, a parfor-loop executes a series of statements over a range of values. Using the parfor command, you can set up a parallel for-loop in your code to explore fixed-point designs by distributing the tests across many computers. In a parfor loop, loop iterations execute in parallel which can provide better performance than standard for-loops.

The test_heart_rate_detector_in_parallel script sets up the system under test and initializes the arrays that will contain the results outside of the parfor-loop. It then uses a parfor loop to test each record in parallel. The parfor-loop loads the data, runs the system, then classifies and saves the results in parallel. When the parfor-loop finishes, the script displays the results.

%% Run test of all records in a database in parallel
record_names = {'ecg_01','ecg_02','ecg_03','ecg_04','ecg_05','ecg_06',...
    'ecg_07','ecg_08','ecg_09','ecg_10','ecg_11','ecg_12','ecg_13'};

%% Set up the system under test
data_type = 'fixedwrap';
T = heart_rate_detector_types(data_type);
[mex_function_name,Fs_target] = setup_heart_rate_detector(record_names,data_type,T);
 
%% Initialize array to contain results 
results_file_names = cell(size(record_names));

%% Test each record in the database in parallel
parfor record_number = 1:length(record_names);
    % Load data
    record_name = record_names{record_number};
    [ecg,tm,ann,Fs] = load_ecg_data(record_name,Fs_target);
    
    % Run system under test
    detector_outputs = run_heart_rate_detector(mex_function_name,ecg,T);
    
    % Classify results
    [qrs_struct,qrs_stats] = classify_qrs(ann, Fs, detector_outputs);
    
    % Save results
    results_file_names{record_number} = save_heart_rate_data(...
        mex_function_name,record_name,...
        data_type,ecg,tm,ann,Fs,...
        detector_outputs,...
        qrs_struct,qrs_stats);

end

%% Display results
display_ecg_results(record_names, results_file_names);

Because loop iterations must be completely independent of each other, you cannot call the save and load commands directly inside a parfor-loop. You can, however, call functions that call these commands. In this example, the functions load_ecg_data and save_heart_rate_data load and save the necessary data.

Description of System Under Test

The system under test in this example tests a simple QRS detector that measures the time difference between QRS detections to compute heart rate. The test_heart_rate_detector_in_parallel script passes ECG recordings to the detection algorithm.

The following plot is an example when the detector algorithm correctly identifies the QRS detections to compute the heartbeat.

The detection algorithm is simplified for this example. Examining the plots and results that are displayed when the example runs shows that the algorithm is not always very accurate.

      Record    #QRS      TP      FP      FN     DER      Se      +P
      ecg_01     253     195       1      58   23.32   77.08   99.49
      ecg_02     133     133      18       0   13.53  100.00   88.08
      ecg_03      94      94       1       0    1.06  100.00   98.95
      ecg_04      92      91       0       1    1.09   98.91  100.00
      ecg_05      93      91       1       2    3.23   97.85   98.91
      ecg_06     131     131      22       0   16.79  100.00   85.62
      ecg_07     174     173       2       0    1.15  100.00   98.86
      ecg_08     117     116      10       1    9.40   99.15   92.06
      ecg_09     137     137       1       0    0.73  100.00   99.28
      ecg_10      96      96       3       0    3.12  100.00   96.97
      ecg_11      73      73       1       0    1.37  100.00   98.65
      ecg_12     146     145      71       0   48.63  100.00   67.13
      ecg_13     144     144       5       0    3.47  100.00   96.64
      Totals    1683    1619     136      62   11.76   96.31   92.25


Legend:
   #QRS: Total number of QRS Complexes
   TP:   Number of true positive
   FP:   Number of false positive
   FN:   Number of false negative
   DER:  Detection error rate in percent
   Se:   Sensitivity in percent
   +P:   Positive prediction in percent

The following plot is an example when the detector algorithm identifies false positives due to noise in the recording.

All ECG recordings used in this example were measured on hobbyist equipment. You can use the PhysioNet database of recorded physiological signals to do a similar analysis on your own. The annotations on these recordings were not verified by doctors.

Run the Example

Run the test_heart_rate_detector_in_parallel example script.

test_heart_rate_detector_in_parallel

References

[1] Patrick S. Hamilton, Open Source ECG Analysis Software (OSEA), E.P. Limited, Somerville, MA, 2002.

[2] Gari D Clifford, Francisco Azuaje, and Patrick E. McSharry. Advanced Methods and Tools for ECG Data Analysis, Artech House, 2006.

[3] American National Standard ANSI/AAMI EC38:2007 Medical electrical equipment — Part 2–47: Particular requirements for the safety, including essential performance, of ambulatory electrocardiographic systems, Association for the Advancement of Medical Instrumentation, 2008.

[4] George B. Moody, "Evaluating ECG Analyzers", WaveForm DataBase Applications Guide, Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, WFDB10.5.23, 13 March 2014.

[5] Ida Laila binti Ahmad, Masnani binti Mohamed, Norul Ain binti Ab Ghani, "Development of a Concept Demonstrator for QRS Complex Detection using Combined Algorithms", 2012 IEEE EMBS International Conference on Biomedical Engineering and Sciences, Langkawi, 17th–19th December 2012.

[6] R. Harikumar, S.N. Shivappriya, "Analysis of QRS Detection Algorithm for Cardiac Abnormalities—A Review", International Journal of Soft Computing and Engineering (IJSCE), ISSN: 2231–2307, Volume–1, Issue–5, November 2011.