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Re: Replacing `find` with logical indexing
Posted:
Jul 9, 2013 10:24 PM


On Wednesday, July 10, 2013 1:20:34 PM UTC+12, dpb wrote: > On 7/9/2013 7:44 PM, Jeff wrote: > > > I am trying to find the smallest nonzero magnitude element of a vector, > > > D. Note that D is not integers. I am eliminating nonzero entries using > > > the `find` command (first line below). The editor says to replace `find` > > > with logical indexing, but replacing `D(find(D))` with `D(D)` returns an > > > error. This is not slowing my code very much, but the editor's warning > > > is mildly bothersome. How do I use logical indexing to fix this? > > > > > > nonZeroD = abs(D(find(D))); > > > > nonZeroD = abs(D(D~0)); > > > > > lambda = max(nonZeroD(nonZeroD == min(nonZeroD))); > > > ICmode = find(D==lambda, 1, 'first'); > > > > > > I also note that the editor doesn't complain about the second `find`. > > > > Depends on what's done w/ the result. In the second you're using the > > truncated version of returning only the first position so logical > > addressing doesn't work so cleanly. > > > > I'm not absolutely positive I follow what you're trying to do but why > > isn't it just > > > > DNZmin=min(abs(D(D~0))); % ? > > > > What's the point of the max(DNZ(DNZ==min(DNZ)))? If you've only > > collected terms in the vector ==min(vector), then the max is the min by > > that selection process. > > > > 
Oh dpb, what a dreadful typist you are....... It should be ~=, not ~: DNZmin=min(abs(D(D~=0)));
And with floating point numbers, shouldn't it be: DNZmin=min(abs(D(abs(D)>tol))); where tol is a small number like 1e6



