My Matlab for loop wont output the matrix I need

[mcquaya]

I'm somewhat new to Matlab and am having issues with a nested "for" and "if" loop. My code is below. This code is combining a binary signal with a cyclic one. I'm trying to create a matrix with the amplitude condition in the first column and in the second column I want the sum of the number of data points where the binary signal reads "1" and the analog cyclic signal's value is above the amplitude condition. I know the if loop works like I want because when I isolate it it gives me the results I want.

The problem is with the for loop. The second column has all the same number when I know they should vary. Every value is equal to what the correct value is for the first row. After the first row every number is the same for some reason.

n=length(stab(:,1));
prob=zeros(2,2);
prob1=zeros(n,1)

for k=1:100
a(k)=k;
for i=1:n
if ((z2(i)>=a(k))||(z2(i)<=-a(k))) && (stab2(i)==1)
prob1(i)=1;
end
prob(k,2)=sum(prob1);
end
prob(:,1)=a;
end

 

[NemoReally]

I'm somewhat new to Matlab and am having issues with a nested "for" and "if" loop. My code is below. This code is combining a binary signal with a cyclic one. I'm trying to create a matrix with the amplitude condition in the first column and in the second column I want the sum of the number of data points where the binary signal reads "1" and the analog cyclic signal's value is above the amplitude condition. I know the if loop works like I want because when I isolate it it gives me the results I want.

The problem is with the for loop. The second column has all the same number when I know they should vary. Every value is equal to what the correct value is for the first row. After the first row every number is the same for some reason.

n=length(stab(:,1));
prob=zeros(2,2);
prob1=zeros(n,1)

for k=1:100
a(k)=k;
for i=1:n
if ((z2(i)>=a(k))||(z2(i)<=-a(k))) && (stab2(i)==1)
prob1(i)=1;
end
prob(k,2)=sum(prob1);
end
prob(:,1)=a;
end

I think (provided I've understood the intent of your code) that your problem is that you don't re-initialize prob1 before every 'i' loop; consequently, it retains the values from the first iteration and, given that a(k) will have lowest 'a' value it will have the highest number of 1s. Setting prob1 to all zeros before the loop should cure the problem.

I'm not a Matlab user, but I think you may be able to do away with the if statement and direct assign the result of your conditional expression to a variable; this would avoid having to reset prob1. I've attached a Mathcad image that shows this method. You may even be able to vectorize the entire expression and avoid the loop altogether.

NR

 

[mcquaya]

Thank you that was very helpful! It's working great now.

 

[NemoReally]

Thank you that was very helpful! It's working great now.

No worries.

 

[alphy]

It's difficult to provide a specific solution without seeing the full code and understanding the purpose of the nested for and if loops. However, here are some general suggestions that may help:

1. Check your variable assignments: Make sure that the variables you are using in the for loop are properly assigned and updated within the loop. For example, in your code, it seems like the variable "prob1" is not being updated within the loop, which could be causing the issue in the second column.

2. Debug your code: Use the debugger in Matlab to step through your code and see how the values of your variables are changing at each iteration of the loop. This will help you identify where the issue is occurring and make necessary changes.

3. Use vectorization: Instead of using nested for loops, consider using vectorized operations in Matlab. This can often be more efficient and less prone to errors. You can read more about vectorization in Matlab's documentation.

4. Check your logic: Make sure that the logic in your if statement is correct and is giving you the desired outcome. You can also try using a different approach to achieve the same result.

5. Seek help: If you are still unable to figure out the issue, consider seeking help from a colleague or posting your code on a forum to get feedback from other Matlab users.

Overall, it's important to thoroughly test and debug your code to identify and fix any issues that may be causing incorrect output.