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Speed ups to the Octave inverse dynamics. #129

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Speed ups to the Octave inverse dynamics. #129

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7646546
myfiltfilt no longer calls rtfilter.m for each sample
tvdbogert Mar 30, 2015
acd711d
Deleted rtfilter.m
tvdbogert Mar 30, 2015
124567c
Added ydd index and removed unecessary semicolon.
moorepants Mar 30, 2015
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38 changes: 27 additions & 11 deletions gaitanalysis/octave/2d_inverse_dynamics/myfiltfilt.m
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Original file line number Diff line number Diff line change
Expand Up @@ -9,28 +9,44 @@
% f0 (scalar) Corner frequency
%
% Outputs
% y (Nsamples x 1) Filtered signal
% yd (Nsamples x 1) First derivative
% ydd (Nsamples x 1) Second derivative
% y (Nsamples x Nchannels) Filtered signal
% yd (Nsamples x Nchannels) First derivative
% ydd (Nsamples x Nchannels) Second derivative

C = 0.802; % correction factor for dual pass 2nd order filter (Winter book)
y = rtfilter_batch(-flipud(t), flipud(x), f0/C); % filter backwards in time
[y, yd, ydd] = rtfilter_batch(t, flipud(y), f0/C); % filter forward in time
C = 0.802; % correction factor for dual pass 2nd order filter (Winter book)
y = filter_batch(-flipud(t), flipud(x), f0/C); % filter backwards in time
[y, yd, ydd] = filter_batch(t, flipud(y), f0/C); % filter forward in time

end
%===================================================================================
function [y, yd, ydd] = rtfilter_batch(t,x,f0)
function [y, yd, ydd] = filter_batch(t,x,f0)
% filters a time series and also returns derivatives
% uses real-time second order Butterworth filter (rtfilter.m)

% some constants we will need
a = (2*pi*f0)^2;
b = sqrt(2)*(2*pi*f0);

% allocate memory for the results
n = size(x,1);
y = zeros(size(x));
yd = zeros(size(x));
ydd = zeros(size(x));

for i = 1:n
[y(i,:), yd(i,:), ydd(i,:)] = rtfilter(t(i),x(i,:),f0);
% Integrate the filter state equation using the midpoint Euler method with step h
% initial conditions are y=0 and yd=0
for i = 2:n
h = t(i)-t(i-1); % time step
denom = 4 + 2*h*b + h^2*a;
A = (4 + 2*h*b - h^2*a)/denom;
B = 4*h/denom;
C = -4*h*a/denom;
D = (4 - 2*h*b - h^2*a)/denom;
E = 2*h^2*a/denom;
F = 4*h*a/denom;
y(i) = A*y(i-1) + B*yd(i-1) + E*(x(i)+x(i-1))/2;
yd(i) = C*y(i-1) + D*yd(i-1) + F*(x(i)+x(i-1))/2;
ydd = (yd(i)-yd(i-1))/h;
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@moorepants moorepants Mar 30, 2015

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Should be ydd(i). I'll push the fix.

end

end
%===================================================================================
%===================================================================================
52 changes: 0 additions & 52 deletions gaitanalysis/octave/2d_inverse_dynamics/rtfilter.m
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