Flipping the numbers 1 to -1

Hi, to all the members. Consider a matrix 'a' now we take a random number, if random number is >= to 0.5 change the first element from 1 to -1 then calculate mag,if not keep it as 1...... then for next step if random number is < 0.5 keep the matrix and calculate mag, now again take random number and check if now the random number is >=0.5 flip the second element calculate mag.......etc keep on going till the 25th element.

for example

a = 1 1 1 1 random = 0.2324 first element remains same mag = 4

now again take random number random = 0.5649 now a becomes a = -1 1 1 1 mag = 2 now again take random random = 0.6978 a = -1 -1 1 1 mag = 0

random = 0.2345 a = -1 -1 1 1 mag = 0

random = 0.7995 a = -1 -1 -1 1 mag = -1

random = 0.3453 a = -1 -1 -1 1 mag = -1

random = 0.9874 a = -1 -1 -1 -1 mag = -4

end the loop

show mag values and plot against B mag = 4 2 0 0 -1 -1 -4

B =linspace(2,0,numel(mag)) plot(B,mag)

thanks for guidance

[Stephen23]

Should those mag = -1 really be -2 ?

[Jos (10584)]

What exactly is your question?

[Offroad Jeep]

I have tried to define the question in explanation.

[Jos (10584)]

Do you have problems coding this? What did you try so far?

[Offroad Jeep]

I have attached the m file........

[Offroad Jeep]

I will be grateful if you can help me in this regard.......... and i think i will be able to solve the problem where i want to fit this logic.......

[Offroad Jeep]

Can you please check the attached problem.

http://www.mathworks.com/matlabcentral/answers/contributors/4899830-4-x-4/questions?s_tid=gn_mlc_ans_myq

Answer 1

[Stephen23]

Try using a while loop:

a = ones(1,4)
k=1;
mag=[];
while k<=numel(a)
    x = rand()>=0.5;
    a(k)=a(k)-2*x;
    mag(end+1)=sum(a);
    k=k+x;
end

Produces:

a =
  -1  -1  -1  -1
mag =
   4   4   2   2   2   0  -2  -4

[Offroad Jeep]

Can i change it for 4 X 4 matrix........

[Stephen23]

Of course you can change it to work with a matrix. If you told me how you want it to work with a matrix then I could help you too! Do you want to work along each row, or column, or along all elements of the matrix (row-wise or column-wise) ?

[Offroad Jeep]

randomly pick the element and flip it from 1 to -1 till all the elements are gone from 1 to -1

[Stephen23]

Well, that is easy to do:

a = ones(4,4);
k=1;
mag=[];
while k<=numel(a)
    x = rand()>=0.5;
    a(k)=a(k)-2*x;
    mag(end+1)=sum(a(:));
    k=k+x;
end

Note the change from a to a(:) so that it works for a matrix too. Here is the output:

>> mag
mag =
    16    16    16    14    12    10    10    10    10     8     6     6     4     2     2     2     2     0     0     0    -2    -4    -6   -8   -10   -10   -10   -12   -14   -14   -14   -14   -16

[Offroad Jeep]

Thanks. Thats great......... will you like to work together for a research paper........

[Stephen23]

If my answer resolves your question then please accept it.

[Offroad Jeep]

Can you please check the attached problem.

http://www.mathworks.com/matlabcentral/answers/contributors/4899830-4-x-4/questions?s_tid=gn_mlc_ans_myq

Answer 2

[Jos (10584)]

help numel
help for
help rand
help if
help sum

% for k=1:N
%  if ...
%     A(k) = -A(k)
%  B(k) = sum ...
% end

[Offroad Jeep]

????????????