Documentation

Overview

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. Running parallel simulations requires a Parallel Computing Toolbox™ license.

Setup

To run this example, copy the example files to a local working directory.

copyfile(fullfile(matlabroot,'help','toolbox','fixpoint', 'examples',...
'parallel_examples','heart_rate_detector'))

In your local working directory, open and run the test file that runs the example.

edit test_heart_rate_detector_in_parallel.m
test_heart_rate_detector_in_parallel

Using Parallel for-Loops For Design Exploration

Like a standard for-loop, a parfor (Parallel Computing Toolbox)-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.

This 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. For more information on the system being tested in this example, see Description of System Under Test.

%% Run test of records in 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. For more information on limitations, see Parallel for-Loops (parfor) (Parallel Computing Toolbox).

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    3.13  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