How can I use a filter in a parfor with the more numerically stable z,p,k?

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Gordon
Gordon 2017-4-26
评论： Gordon 2017-4-28
Hello,
I would like to use a filter in a parfor loop. Using [b,a] coefficients there is no problem. Because of a better stability I have to use the [z,p,k] coefficients. It perfectly works in a for loop. However, in a parfor loop the error massage "Not enough input arguments." appears. Does anyone know a workaround?
Here is a little example: Anything works but the last loop!
% Signal
x = sin(0:pi/1000:10*pi);
% Filter properties
N = 1;
fc = 1/(2*pi);
fs = 1000/pi;
Wn = fc/(fs/2);
ftype = 'low';
% Transfer Function design
[b,a] = butter(N,Wn,ftype);
% Zero-Pole-Gain design
[z,p,k] = butter(N,Wn,ftype);
[sos,g] = zp2sos(z,p,k);
hd = dfilt.df2tsos(sos, g);
%%Loops
for n=1:2
y = filter(b,a,x);
end
parfor n=1:2
y = filter(b,a,x);
end
for n=1:2
y = filter(hd, x);
end
parfor n=1:2
y = filter(hd, x);
end

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Aniruddha Katre
Aniruddha Katre 2017-4-26
Modifying the parfor loop as follows seems to resolve the error. The filter object was causing the error to occur for some reason, but creating the filter object on each worker separately fixes it.
parfor n=1:2
hd = dfilt.df2tsos(sos, g);
y(n,:) = filter(hd, x);
end
  2 个评论
Edric Ellis
Edric Ellis 2017-4-27
There's an underlying problem sending objects of type dfilt.df2tsos into parfor loops. An additional workaround you can use to avoid re-creating the object on each iteration is:
hdc = parallel.pool.Constant(hd);
parfor ...
... = filter(hdc.Value, ...);
end

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