Vectorize a code that finds the roots of polynomials stored in matrices

Question

Naveen 2013-2-6

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I need some tips on how to vectorize a code that finds the roots of polynomials stored in matrices. What I have is a multidimensional array that contains 100 matrices of 100-by-3 size. I'm pasting the code below

 one = ones ( 100, 100 );
 poly.struc = reshape( [ one; gr_fac1; - gr_fac2 ], 100, 3, [] ); 
 poly_roots_select = zeros ( 100, 100);
 for j = 1:1:100
 poly_matrices = poly.struc ( :, :, j );
    for i = 1:1:100
      poly_select = poly_matrices ( i, : );
      poly_roots = roots ( poly_select );
      poly_roots_select ( i , j)  =  poly_roots ( real ( poly_roots) > 0 , 1 ) ; 
    end
 end

I would like to remove both for loops. At minimum I like to be able to access the matrices stored in poly.struc array without putting a loop for this. Is there also any other way to be able to pass a row vectors from a matrix to roots function without needing a loop?

Thanks in advance

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Answer 1

Thorsten 2013-2-7

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https://ww2.mathworks.cn/matlabcentral/answers/62466-vectorize-a-code-that-finds-the-roots-of-polynomials-stored-in-matrices#answer_74130

在 MATLAB Online 中打开

The roots function only accepts vectors.

You may speed up your code by getting rid of the two intermediate variables poly_matrices and poly_select:

 for j = 1:1:100
    for i = 1:1:100
      poly_roots = roots ( poly.struc ( i, :, j ) );
      poly_roots_select ( i , j ) = poly_roots ( real ( poly_roots) > 0 , 1 ) ; 
    end
 end

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Naveen 2013-2-7

Thanks for your suggestions! So you think that in this program, it's not possible to remove for loops? I was thinking to get rid of at least one for loop by passing this poly.struc as an argument to a function which also accept index j as other argument. Before I make a call to the function, I can vectorize j and hopefully function would take the vectored j as an argument. Inside this function, I can use one for loop to calculate the roots. What do you think?