How to define RDT function in Matlab?

I used following code for my calculations but I think it has an error.

Code

function [R,t] = RDT(y,ys,T,dt)

%

% [R] = RDT(y,ys,T,dt) returns the free-decay response (R) by

% using the random decrement technique (RDT) to the time serie y, with a

% triggering value ys, and for a duration T

%

% INPUT:

% y: time series of ambient vibrations: vector of size [1xN]

% dt : Time step

% ys: triggering values (ys < max(abs(y)) and here ys~=0)

% T: Duration of subsegments (T<dt*(numel(y)-1))

% OUTPUT:

% R: impusle response function

% t: time vector asociated to R

%

% Author: E. Cheynet - UiB - last modified 14-05-2020

%%

if T>=dt*(numel(y)-1)

error('Error: subsegment length is too large');

else

% number of time step per block

nT = round(T/dt); % sec

end

if ys==0

error('Error: ys must be different from zero')

elseif or(ys >=max(y),ys <=min(y)),

error('Error: ys must verifiy : min(y) < ys < max(y)')

else

% find triggering value

ind=find(diff(y(1:end-nT)>ys)~=0)+1;

end

% construction of decay vibration

R = zeros(numel(ind),nT);

for ii=1:numel(ind)

R(ii,:)=y(ind(ii):ind(ii)+nT-1);

end

% averaging to remove the random part

R = mean(R);

% normalize the R

R = R./R(1);

% time vector corresponding to the R

t = linspace(0,T,numel(R));

end

Error msg

>> RDT

Not enough input arguments.

Error in RDT (line 18)

if T>=dt*(numel(y)-1)

can anybody suggest me a solution for this problem?

Thank You.!

[Jon]

You can use the code button on the MATLAB Answers toolbar to nicely format your code.

[E. Cheynet]

Hi Hasantha,

There is a Matlab livescript on Matlab File Exchange, which shows how to use the function RDT: https://se.mathworks.com/matlabcentral/fileexchange/55557-damping-ratio-estimation-from-ambient-vibrations-sdof?s_tid=srchtitle

Answer 1

[Jon]

You need to call the function with its arguments.

You just typed rdt on the command line. You must first assign the variables y,ys, T, and dt and then type on the command line:

R= rdt(y,ys,T,dt)

Note it is not necessary to use the same variable names on the command line as in the function definition, so assuming a,b,c and d were assigned appropriate values you could also call the function using

R= rdt(a,b,c,d)

[Jon]

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