How can I modify the code to get the sensors with the positions that fulfill the conditions below?

function [Rhoc,Alfac,Rhoc2,Alfac2]= TheRightSensors(W,n,R)

for i=1:n
  
  %R is the Radius of the disk where the sensor nodes are positioned. The center of the disk is P and radius is R.
  
  %Other sensors are put in the disk D(P,2R)
  
  delta=R/6; %delta is a threeshold parameter set to filter out the nodes far away from the critical trajectory
  
  rhoi=randi(W);% rho is the radius of each sensor which is random, and the max limit is W,
  %rhoi is suposed to be a vector that contains the values  of radius for
  %the n sensors
  
  Alfai=randi(2*pi); % Alfa is the angle that defines the position of the sensor and takes
  %ranndom values between 0:2*pi for n sensors
  
  if rhoi-R<delta %We are interested for sensors that fulfill this condition
    
    Rhoc=rhoi; %Contains the radiuses of the selected sensors
    
    Alfac=Alfai; %Contains the angles of the selected sensors
    
    if Alfai-Alfac > 2*Theta %After the first selection of the sensors, we select again the sensors
      %that fulfill the condition of the angle
      
      Alfac2=Alfac; %Alfac2 is supposed to be a vector that
      %saves the angles of the sensors that fulfill the condition
      
      Rhoc2=Rhoc; %Rhoc2 is supposed to be a vector that
      %saves the radius of the sensors that fulfill the condition
      
    end
  end
  %Based on the outputs, we can define the filtered sensors

[Jan]

Please do not post multiple threads for one problem, because this confuses the readers. Thanks.

[Jenny]

I understand and I apologise for the confusion. This is the last one. Before I was trying to solve it by taking into consideration only 10 nodes, but it is not a valid solution. The solution should be for n nodes. If someone can help, I would be so thankful.

[Jenny]

Jan could you please help me to modify the code above to do realize the functions explained in the comments? Thanks.

Answer 1

[Walter Roberson]

You have

rhoi=randi(W);% rho is the radius of each sensor which is random, and the max limit is W, %rhoi is suposed to be a vector that contains the values of radius for %the n sensors

That would be the case for

rhoi=randi(W, 1, n);% rho is the radius of each sensor which is random, and the max limit is W, %rhoi is suposed to be a vector that contains the values of radius for %the n sensors

This assumes that you want discrete positive integer values for the radii.

[Jenny]

Thank you very much for the suggestion. If there is any other mistake in my code, please help me correct them.

[Walter Roberson]

You have

if rhoi-R<delta

if rhoi is a vector then this will not work for you. You need to either loop through the elements or use logical indexing.

[Jenny]

How can I do it? :/

[Walter Roberson]

Your code is confusing. You have

Alfac=Alfai; %Contains the angles of the selected sensors
    
    if Alfai-Alfac > 2*Theta %After the first selection of the sensors, we select again the sensors
      %that fulfill the condition of the angle

Theta is not defined in your code.

You assigned Alfac=Alfai, which would seem to indicate that Alfac and Alfai would be identical. In that case, Alfai-Alfac would be a vector of zeros, and that would only be > 2 * Theta if Theta is negative.

Your comments hint about selecting a subset of sensors. If Alfac is only intended to contain a subset of Alfai, then it is not clear what Alfai-Alfac is intended to mean: the full list of sensors minus a subset?? A subset minus the same subset ?? Are you trying to do something like for each sensor, find all of the sensors that are within 2*Theta angle? Are you trying to do something like for each sensor, determine whether any of the sensors are within 2*Theta angle? But the sensor would be within that angle of itself, so are you trying to determine whether there is any other sensor within that angle ??

I figure that your outputs Rhoc and Alfac are intended to be vectors of radius and corresponding values, and that perhaps Rhoc2 and Alfac2 are intended to be vectors as well, but if Rhoc2 and Alfac2 are intended to be subsets of Rhoc and Alfac then it is not obvious to me that knowing the values separately would be the best: it would seem more useful if third output of the function were perhaps a vector which could be used to index Rhoc and Alfac, an indicator of which of the pairs satisfied the conditions.

[Jenny]

Ok. We take theta=pi/8. You are right. Now I saw the mistake with the angle. The difference of angles of the selected k sensors defined by Alfac&Rhoc should not be > 2theta, so we reselect sensors with Alfack-Alfack+1<2*theta Thanks a lot for your patience and help. If you can help tonight to correct the mistakes, I would really appreciate it so much. Thanks again.

[Jenny]

Alfac is supposed to contain the angles of the selected sensors based on the first condition. Maybe it is not correct to say Alfac=Alfai. How can I save the values of the sensors that fulfill the condition in a new vector then because I don't know how to do it? I am a beginner in Matlab, and I know that I have made mistakes in the code. This is why I am asking for help you who know very well how to solve matlab problems.

[Walter Roberson]

I am stuck on the question of which angle is to be calculated? Is that Alfac(k) - Alfac(k+1) < 2*theta ? Does that imply that the last sensor is never to be selected or always to be selected since there would not be a next sensor to compare against?

Is it possible that you want abs(Alfac(k) - Alfac(k+1)) < 2*theta instead?

With the angles being random, it is entirely possible that you have a situation like "small" "big" "big" where the angle between the first two is greater than the threshold but the angle between the second and third is within range, resulting in a sensor being selected for being within the desired angle range of a sensor that was not selected. It is not at all clear to me that is desired.

I do not understand why you are going through this process of generating random locations and then throwing away items that are outside the criteria. Why not just generate a random starting point and then generate each item sequentially from there, ensuring that it is within range of the previous item ?

[Jenny]

Yes, i want the the abs(Alfac(k) - Alfac(k+1)) < 2*theta

Walter, it is clear that you have a better idea to solve this problem, so please if you can, could you give the solution you think is the right one? In this way we avoid my mistakes. :) I really appreciate your help. Thank you so much.

[Walter Roberson]

There has not been any problem statement so I do not know what the goal is.

[Jenny]

It is not necessary to do the full code.

Even if you help me to do a part of it that gives some results is enough. I have tried, but I made many mistakes. :/

[Walter Roberson]

Notice that the positions are input, not randomly generated within the algorithm. This is a matter of refining nodes that are already known.

I am not clear on the notation for Di(Pi,2R): a disk of some sort with radius (or diameter?) 2R but the Pi I do not understand at the moment. Given that they exist within a disk a pair of coordinates would be needed.

Step 1 builds polar coordinates within each hexagon, so it is not the original absolute coordinates that are being acted upon for the steps following that.

When they talk about picking from the spare nodes, it is not clear which nodes are spare. I have to guess that they are referring to the nodes that have not been selected under the criteria that |rho_S_i - R| <= delta

[Jenny]

This image shows the disk with the center Pi and sensors around. Pi, or P, is the center. However you understand it, I am sure it is better than how I understood it, so don't worry to give me the most precise code result. Thanks so much.

[Jenny]

Walter, please if you can help create a code by ignoring the fact that the zone H should be divided in Hi hexagons. Just take a hexagon with center P. The center has around n sensors and based on the conditions there will be selected some sensors at the end, that we want to be awake to cover the zone. I don't know how to put the sensors that fulfill the condition in another vector,and I don't know how to access them in order to apply the conditions in them.

[Walter Roberson]

You are asking me to do all the essential work, but that is not something that interests me.

Generate some random points in cartesian coordinates. Find their centroid and call that P = (Px, Py) . Subtract that centroid from all of the other coordinates to get relative (x,y) coordinates for each. Convert to polar notation. Now sort those according to the angle. Proceed with the filtering.

[Jenny]

Ok. But can you help me only with the right code that will apply the condition in the vector, and save the sensors that fulfill the condition in another vector?