Query in applying If command

Question

Prakhar Modi 2019-9-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/482038-query-in-applying-if-command

评论： Prakhar Modi 2019-9-26

Hello everyone,

First i'll write the part of the code than I'll ask the doubt.

O=1:25;
n=randn(100,1);
for j=1:10
  for i=1:length(n)
    G(j)= a+ b*n(i);
    if (abs(G(j)-O(:))<1)
      n(i)=[ ]
      break
    end
  end
end

SO here you can see I need to generate G on the basis of a and b and n(random number generated). The value of G(j) shall be near to O for which I have used the if command.

Now if I want to generate 10 values of G, so My doubt are:

1) Is [abs(G(j)-O(:))<1 ] correct? I want that [abs(G(j)-O(:))<1] with any one of the 25 values of O. Then before going to next iteration of j, I am removing the n(i) which is used to generate G(j) in last iteration and similarly i want to remove the value of O which is used in last iteration. So what I want is that when I run the next iteration there will be one less value in O and n after every iteration which is used in previous iteration.

2) How to remove the particular value of O which is used in previous iteration before going to next iteration.

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KALYAN ACHARJYA 2019-9-25

"a" is undefined??

G(j)= a+ b*n(i);

Prakhar Modi 2019-9-25

a has some value let say a= 7.5.

I just need to know how to check the if condition for all observed data but whichever value the particular iteration is using should be removed before next iteration.

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Answer 1

Jan 2019-9-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/482038-query-in-applying-if-command#answer_393456

if (abs(G(j)-O(:))<1)

The if command needs a scalar condition. Therefore Matlab inserts an all() to evaluate the vector G(j)-O(:) < 1. Are you sure, that this is wanted. Then write it explicitly to avoid confusions.

This canniot work: n(i)=[ ]. After you have removed the element n(i), the vector n is shorter. Then you cannot access all elements until 100.

What about this:

O = 1:25;
a = 7.5;
for k = 1:10
    match = false;   
    while ~match
       x = a + b * randn;
       n = find(abs(x - O) < 1);
       if ~isempty(n)
          match = true;
          O(n)  = [];
       end
    end
    G(k) = x;
end

This is inefficient. There is no guarantee, that e.g. the last value of O matchs a random number in a finite amout of time. Maybe it is better, if you explain the problem you want to solve.

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Prakhar Modi 2019-9-26

Thanks for the reply.

But n(i)=[ ] is working and I need to remove it for the next iteration and I want that in next iteration it should access 99 elements. And similarly I need that it should remove 1 element out of 25 element of O which is used, so that in next iteration it will only have remaining 24 elements.

can you suggest me that how the code will check the if condition for all elements of O one by one and whenever it satisfies it removes that element of O before next iteration.

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