MATLAB: Vectorization of multiple embedded for loops

MATLABvectorization

I have the following code that includes 3 iterated for loops in order to create an upper diagonal matrix, I plan on performing on large data set many times and want to make as computationally efficient as possible.

data = magic(3);
n = size(data,1);
W = zeros(n,n);
for i = 1:n
  for j = i:n
    if i==j
      www(i,j)=0;
    else
      for k = 1:n
        temp(1,k) = (data(i,k)-data(j,k))^2;
        sumTemp = sumTemp + temp(1,k);
      end
      W(i,j)=sqrt(sumTemp);
    end
    temp = 0;
    sumTemp = 0;        
  end
end

Answer should look like:

[0 6.4807 9.7980
0 0 6.4807
0 0 0]

I am working it hard right now, but figure I would throw it out there in case anyone has any suggestions that would save me hours of fiddling around. Thanks in advance.

Keith

Best Answer

W = triu(squeeze(sqrt(sum(bsxfun(@minus,data,permute(data,[3 2 1])).^2,2))));

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MATLAB: Help modifying a User-defined-function

try something like the following code. Save this in a single file named zero_cross.m

function [temp80,temp78,NT]=zero_cross(x,N,dt)
    m = size(x,2); % num columns
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    temp78 = cell(1,m);
    NT = cell(1,m);
    for i=1:m
        [temp80{i}, temp78{i}, NT{i}] = zero_cross1(x(:,i), N, dt);
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function [temp80,temp78,NT]=zero_cross1(x,N,dt)
% find zero-crossing points
   temp70 = x(1:N-1).*x(2:N);
   temp70(N) = 1.0;
   temp72=find(temp70<0);
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MATLAB: Issues with the jacobian method code

Just a small error in your code. Here's the correction:

 function [x] = jacobi(A,b,x0,n_iter)
n=length(x0);
 x = zeros(size(x0)); 
for k=1:n_iter
      for i=1:n
          temp=0;
          for j=1:n
              temp=temp+A(i,j)*x0(j); %you should use x0(j) here, not x(j)
          end
          temp=temp-A(i,i)*x0(i);
          x(i)=(1/A(i,i))*(b(i)-temp);
      end
      x0=x;
end
  disp(x)
end

However, you could also do it like this:

function [x] = jacobi(A,b,x0,n_iter)
n=length(x0);
 x = zeros(size(x0)); 
for k=1:n_iter
      for i=1:n
          temp=0;
          inds = [1:i-1, i+1:n];
          temp = A(i,inds)*x0(inds);
          x(i)=(1/A(i,i))*(b(i)-temp);
      end
      x0=x;
end
  disp(x)
end

Best Answer

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MATLAB: Help modifying a User-defined-function

MATLAB: Issues with the jacobian method code

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