matrix indexcing in compare with two matrices

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

Answer 1

[Guillaume]

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);

[fatema saba]

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]

Ah, ok. You should given that explanation from the beginning. The simplest way to do this:

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]
validindices = setdiff(1:numel(a), [find(a); find(b); find(c)]);
pick = randperm(numel(validindices), 6); %6 indices to pick
d = zeros(size(a));
d(validindices(pick)) = 1

Basically, use setdiff to get the indices you can pick from (set difference of all indices minus the ones already used in a, b and c) and pick 6 from there.

[fatema saba]

Thank you but when I use

pick=randperm(numel(validindices),6)

I got this error

??? Error using ==> randperm

Too many input arguments.

[Guillaume]

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]

Thank you for your kindness