MATLAB Answers


Query in applying If command

Asked by Prakhar Modi on 25 Sep 2019
Latest activity Commented on by Prakhar Modi on 26 Sep 2019
Hello everyone,
First i'll write the part of the code than I'll ask the doubt.
for j=1:10
for i=1:length(n)
G(j)= a+ b*n(i);
if (abs(G(j)-O(:))<1)
n(i)=[ ]
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.


"a" is undefined??
G(j)= a+ b*n(i);
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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1 Answer

Answer by Jan
on 25 Sep 2019

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) = [];
G(k) = x;
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.

  1 Comment

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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