Math Forum Discussions

dwi

Posts: 15
Registered: 10/18/12

Re: sum of exponentials
Posted: Nov 23, 2012 12:01 PM

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"dwi" wrote in message <k8o5ro$6ae$1@newscl01ah.mathworks.com>...
> "dwi" wrote in message <k8o3vo$ia$1@newscl01ah.mathworks.com>...
> > "dwi" wrote in message <k8o2mg$pdp$1@newscl01ah.mathworks.com>...
> > > "Roger Stafford" wrote in message <k8lqar$4po$1@newscl01ah.mathworks.com>...
> > > > "dwi" wrote in message <k8l6sb$2fj$1@newscl01ah.mathworks.com>...
> > > > > I have a matrix whose data are interrupted by sequences of zeros. I need every time that there's a zero value to substitute it with a sum of exponentials using the previous data, eg:
> > > > > x=[x1 x2 x3 0 0 0 x7 0 0]
> > > > > When i find the first zero in the element x4 I want:
> > > > > x4=(x3*e^(-1)+x2*e^(-2)+x1*e^(-3))/(e^(-1)+e^(-2)+e^(-3));
> > > > > However, when I find the second zero value I need to calculate the same expression but without using the previous recalculated values. That is,
> > > > > x4=x5=x6
> > > > > and for x8 I will use only the values in x7,x3,x2,x1 and then x8=x9 etc
> > > > > And all this for a 180000-length data.
> > > > > Any ideas on how to do this?
> > > > > Thanks in advance
> > > > - - - - - - - - -
> > > > a = 0; b = 0;
> > > > for k = 1:length(x)
> > > > if x(k) ~= 0
> > > > a = x(k) + a*e^(-1);
> > > > b = 1 + b*e^(-1);
> > > > else
> > > > x(k) = a/b;
> > > > end
> > > > end
> > > >
> > > > Roger Stafford
> > > Thank you for your answer but if I use this the index of the exponent never changes.I want it to decrease as k increases, and i don't know hot to calculate a sum like this.
> >
> > A correction:
> > x8=(x7*e^(-1))/e^(-1)
> > ie without using x1,x2,x3 but only the immediate previous non-zero values
>
> This is what I have so far:
> s=0;
> s1=0;
> i=1;
> while i<=length(x)
> for j=1:length(x)
> if x(i)~=0
> s=s+???? %%%%%the numerator which I still don't know how to calculate
> s1=s1+e^(-j);
> i=i+1;
> else
> x(i)=s/s1;
> i=i+1;
> j=1;
> s=0;
> s1=0;
> end
> end
> end
> This seems to work fine for the denominator. ANy ideas about the numerator?
It doesn't work though if I have subsequent zeros as it devides with zero when I set s1=0 inside the if..I'm at a loss