MATLAB: Matrix reduction

matrix reduction

I have a very large set of data of over 1000 readings in [A]. I need to reduce the data to 101 readings evenly spaced over the original data set. Can anyone give me some help, or point me in the right direction? Any help would be much appreciated.

Best Answer

If DAT is your original data.

NewDAT = DAT(round(linspace(1,length(DAT),101)))

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MATLAB: Recursive Matrix Row Reduction

Ok, I have your solution.

1. Your subtract function in the beginning did not return the subtraced matrix.

2. You needed to return the previously calculated matrix (as I commented in the first response). However, since the returned matrix is smaller than the current matrix, you have to account for that.

3. The whole pivot point vector is not needed. The current pivot point is calcuated in the beginning of each cycle, meaning that when later on you need to subtract out the other values of the current row, you just use the current row.

Now, in the solution, I assumed that you wanted the generalized format for solving systems of non-zero equations.

I.e. The format of the input M is assumed to be

[matrix A] = [Column solution B] - such that the last column of the input matrix is the vector B.

I'm using an older verion of matlab, so I commented out some of your debugging to make it easier on myself.

if isempty(M)
    disp('found empty');
    %     pivots = [];
    return;
end        %Find size of Matrix, calculate tolerance level
[rows,cols] = size(M);
tolerance = length(M)*norm(M)*eps;
%Find the pivot variable - it is value x, at position p
[x,p] = max(abs(M(:,1)));
if x>tolerance
    M = Exchange(M,1,p);
    M = Divide(M,1,M(1,1));
    for i=2:rows
        if M(i,1)==0
            %do nothing
        else
            M = Subtract(M,1,i,M(i,1)/M(1,1));
        end
    end
    disp('Recurring now.');
    [new_sub_matrix] = echelon(M(2:rows,2:cols));
    disp('Getting out of the recursion, M is...');
      if(~isempty(new_sub_matrix))
          %check to make sure the sub matrix exists - cannot add an empty
          %matrix
          M(2:rows,2:cols) = new_sub_matrix;
      end
      disp(M);
          %we index over colums, but we count based on the # rows
          for z=2:rows
              %         currentpivot = pivots(z);
              subtract_factor = M(1,z);
              M = Subtract(M,z,1,subtract_factor);
          end
  %     end

      fprintf('Check on m\n');
      disp(M);
      % else
      %     disp('the else has been called.');
      %     [new_sub_matrix,newpivots] = echelon(M(:,2:cols));
      %     for z=1:length(newpivots)
      %         pivots(end+1) = newpivots(z) + 1;
      %     end
  end
  disp('At the end of the function, M is...');
  disp(M);

Best Answer

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