is there a way to call vectors one by one from matrix other than "for" loop?

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hengzh47 2015-3-29

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关闭： MATLAB Answer Bot 2021-8-20

I have a matrix [a1,a2,a3,a4; b,b,b,b; c,c,c,c], now I want to call each column for a pre-defined function f(a,b,c). There result will be 4x1 vector. I know how to do this with "for" loop, just wondering if there is a way to vectorize the calculation so that don't need to use the loop.

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Answer 1

Matt J 2015-3-29

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编辑：Matt J 2015-3-29

Not for a general function f(). There are ways to hide the for-loop using arrayfun(), but that's not genuine vectorization.

Depending on the form of f(), however, you may be able to pass the entire matrix to f() and have it return a 4xN result whose columns are computed in a vectorized way. We would have to see the definition of f() to say more.

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Matt J 2015-3-29

编辑：Matt J 2015-3-29

That function does not look like it produces a 4x1 output. It looks like it returns a scalar. Where are a,b,c?

Matt J 2015-3-29

编辑：Matt J 2015-3-30

在 MATLAB Online 中打开

In any case, you can certainly do more vectorization within the for-loop, so that matrix-valued y can be handled

      [m,n]=size(y);
      h=zeros(m,n);
      h(1,:)=omega;
      for t=1:m   %loop over rows of y
        last=h(t-1,:);
        h(t,:)=omega + alpha * last.*((y(t-1,:)-r)./sqrt(last)-lambda-gamma).^2 ...
               + beta * last;
      end