43 lines
2.5 KiB
Matlab
43 lines
2.5 KiB
Matlab
function [ResultStruct] = AutocorrStrides(data,FS, StrideTimeRange,ResultStruct);
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%% Stride-times measures
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% Stride time and regularity from auto correlation (according to Moe-Nilssen and Helbostad, Estimation of gait cycle characteristics by trunk accelerometry. J Biomech, 2004. 37: 121-6.)
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RangeStart = round(FS*StrideTimeRange(1));
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RangeEnd = round(FS*StrideTimeRange(2));
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[AutocorrResult,Lags]=xcov(data,RangeEnd,'unbiased');
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AutocorrSum = sum(AutocorrResult(:,[1 5 9]),2); % This sum is independent of sensor re-orientation, as long as axes are kept orthogonal
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AutocorrResult2= [AutocorrResult(:,[1 5 9]),AutocorrSum];
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IXRange = (numel(Lags)-(RangeEnd-RangeStart)):numel(Lags);
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% check that autocorrelations are positive for any direction,
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AutocorrPlusTrans = AutocorrResult+AutocorrResult(:,[1 4 7 2 5 8 3 6 9]);
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IXRangeNew = IXRange( ...
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AutocorrPlusTrans(IXRange,1) > 0 ...
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& prod(AutocorrPlusTrans(IXRange,[1 5]),2) > prod(AutocorrPlusTrans(IXRange,[2 4]),2) ...
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& prod(AutocorrPlusTrans(IXRange,[1 5 9]),2) + prod(AutocorrPlusTrans(IXRange,[2 6 7]),2) + prod(AutocorrPlusTrans(IXRange,[3 4 8]),2) ...
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> prod(AutocorrPlusTrans(IXRange,[1 6 8]),2) + prod(AutocorrPlusTrans(IXRange,[2 4 9]),2) + prod(AutocorrPlusTrans(IXRange,[3 5 7]),2) ...
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);
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if isempty(IXRangeNew)
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StrideTimeSamples = Lags(IXRange(AutocorrSum(IXRange)==max(AutocorrSum(IXRange)))); % to be used in other estimations
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StrideTimeSeconds = nan;
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ResultStruct.StrideTimeSamples = StrideTimeSamples;
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ResultStruct.StrideTimeSeconds = StrideTimeSeconds;
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else
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StrideTimeSamples = Lags(IXRangeNew(AutocorrSum(IXRangeNew)==max(AutocorrSum(IXRangeNew))));
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StrideRegularity = AutocorrResult2(Lags==StrideTimeSamples,:)./AutocorrResult2(Lags==0,:); % Moe-Nilssen&Helbostatt,2004
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RelativeStrideVariability = 1-StrideRegularity;
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StrideTimeSeconds = StrideTimeSamples/FS;
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ResultStruct.StrideRegularity_V = StrideRegularity(1);
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ResultStruct.StrideRegularity_ML = StrideRegularity(2);
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ResultStruct.StrideRegularity_AP = StrideRegularity(3);
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ResultStruct.StrideRegularity_All = StrideRegularity(4);
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ResultStruct.RelativeStrideVariability_V = RelativeStrideVariability(1);
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ResultStruct.RelativeStrideVariability_ML = RelativeStrideVariability(2);
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ResultStruct.RelativeStrideVariability_AP = RelativeStrideVariability(3);
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ResultStruct.RelativeStrideVariability_All = RelativeStrideVariability(4);
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ResultStruct.StrideTimeSamples = StrideTimeSamples;
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ResultStruct.StrideTimeSeconds = StrideTimeSeconds;
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end |