matrix indexcing in compare with two matrices

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fatema saba 2015-1-17

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评论： fatema saba 2015-1-17

采纳的回答： Guillaume

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Hello

I have 3 matrices:

m_z=[1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0]

m_y=[19 6 21 16 5 17 3 25 9 20 8 24 15 11 12 4 23 7 14 13 18 2 1 10 22]

m_x=[9 13 14 17 1 2 3 8 21 6 11 12]

I want to run

A=m_z(m_y)

except about the numbers that are in m_x. about these numbers, elemnts of matrix A must be zero.

Thank you very much

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Answer 1

Guillaume 2015-1-17

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Wouldn't this do what you want:

m_z(m_x) = 0; %set elements m_x of m_z to 0 so when they're indexed by m_y they return 0
A = m_z(m_y);

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fatema saba 2015-1-17

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No, in fact matrix m_x is come from the index of cells that are located by 1 in matrices a, b, c (in my following code)

from my code you can find that number of elements 1 in matrix a , b and c are 4, 3 and 5 respectively.

I want to create matrix d randomly with 6 elements 1 in cells that have not been filled by one before with matrix a and b and c.

I think at the end of my code if I eliminate the number of cells that are located with 1 in matrix a and b and c from m_y I can create matrix d.

if true
  function[d]=random(d_area)
a=[0 0 0 0 0;0 0 0 1 0;0 0 1 0 0;0 1 1 0 0;0 0 0 0 0]
b=[1 0 0 0 1;1 0 0 0 0;1 1 0 0 0;0 0 0 0 0;0 0 0 0 0]
c=[0 1 1 0 0;0 0 1 0 0;0 0 0 0 0;0 0 0 0 0;0 0 0 0 0]
[m n]=size(a)
aa1=numel(find (a>0))
bb1=numel(find (b>0))
cc1=numel(find (c>0))
d_area=6   %number of elements that must be 1 in matrix d
A1=aa1+bb1+cc1+d_area
aa2=numel(find(find((a>0))>A1))
bb2=numel(find(find((b>0))>A1))
cc2=numel(find(find((c>0))>A1))
B=aa2+bb2+cc2
A=A1-B
dimen=m*n;
    m_y=randperm(dimen);
    z1=[ones(1,A), zeros(1,dimen-A)];
    z=reshape(z1,m,n)
    d1=a+b+c+z

d end

Guillaume 2015-1-17

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You must have a fairly old version of matlab, then. The two argument version of randperm has been available since R2011b. Just use randperm with 1 argument and use the first 6 elements.

pick = randperm(numel(validindices);
pick = pick(1:6);

fatema saba 2015-1-17

Thank you for your kindness

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matrix indexcing in compare with two matrices

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matrix indexcing in compare with two matrices

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