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Scaling the natrix in specific range

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kash
kash 1 Dec 2012
편집: Walter Roberson 18 Apr 2017
I have a 300x1 matrix
where the minmum value is
-2.1188e+003
maximum is
460.3171
i want to scale in region from -1 to 1

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답변(2개)

Nasser M. Abbasi
Nasser M. Abbasi 1 Dec 2012
Since I just wrote the code, might as well post it. A quick function to scale it
function C = nma_rescale(A,new_min,new_max)
%Nasser M. Abbasi 011212
%NO ERROR CHECKING DONE ON INPUT. Rescale a matrix or a vector A
current_max = max(A(:));
current_min = min(A(:));
C =((A-current_min)*(new_max-new_min))/(current_max-current_min) + new_min;
end
to use:
EDU>> C=rand(3);
EDU>> B=nma_rescale(C,-1,1)
B =
-0.7625 0.8960 -0.2033
-0.3188 -0.8938 -1.0000
-0.8317 1.0000 -0.3316

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Dario Dematties
Dario Dematties 18 Apr 2017
Hello, with respect to the solution proposed by Nasser M. Abbasi. What should I do when current_max=current_min? What is the conventional way to solve this problem?
Jan
Jan 18 Apr 2017
@Dario: There is no convention. It depends on your problem, if the result of a scaled scalar is -1, 0, +1 or Inf, perhaps NaN.
Dario Dematties
Dario Dematties 18 Apr 2017
Thanks Jan, Does anyone know which is the reaction of libsvm software on matlab when it is fed with vectors with missing data (NaN)?

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Walter Roberson
Walter Roberson 1 Dec 2012
편집: Walter Roberson 1 Dec 2012
Does 0 need to remain 0, or should it become the midpoint of your [-2118.8 to 460.317] range?
0 remains 0:
matmin = min(mat);
matmax = max(mat);
newmat = mat;
newmat(mat < 0) = mat(mat < 0) ./ abs(minmat);
newmat(mat > 0) = mat(mat > 0) ./ maxmat;
Midpoint becomes 0:
matmin = min(mat);
matmax = max(mat);
newmat = 2 * (mat - matmin) ./ (matmax - matmin) - 1;

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