Nested For loops- Pleeease HELP!!

Hi! Hope you guys are doing great! :) Well this is a very trivial problem I am facing but I dont know I am totally stuck.. Can't figure out where the problem is!!

Well I have two arrays (or matrices) out_M and out_R (just attached the text files with this question.. I have simply written this code:

*for j=1:1:11

     val = out_R(j,1);

     for k=1:1:107

          if out_M(k,1) == val
          out_M(k,2) = out_M(k,2)-out_M(1,2);
          end
     end
end*

And I guess you must have noticed what I try to do.. I just want to take the first column value from out_R and then enter the out_M matrix. Then I just compare the first column value of out_M with the first column value of out_R. Till these values match, I just want to subtract a fixed number from the second column values of out_M.

Thats it!! All the counters are incrementing absolutely fine!! but the result only appears for 1 cycle not the 107 cycles.. :( its getting frustrating..

Please guide me as to what is wrong!

Thank you so much!

cheers

Pramit

Answer 1

[Titus Edelhofer]

Hi Pramit,

if I take a look at out_M, then in the first entry you have zero. That's where you enter the "if" condition. All other values of out_M are different from all values of out_R, so you will never again enter into the if condition.

That said, I don't understand what you want to achieve, unfortunately, so I can't help more than the above. Try to formulate differently or in more detail.

Titus

[pramit Sood]

Aah really sorry Titus!

Well please find attached the corrected out_M matrix. That zero was a mistake.. Here's the code again:

for j=1:1:11 // Here I enter the out_R matrix and pick up first value at out_R(1,1) for instance

     val = out_R(j,1); //here I store this first value in 'val' - for 
                         instance - out_R(1,1) = 0

     for k=1:1:107  /this is the nested for loop. I enter the out_M matrix.

          if out_M(k,1) == val  //compare the first column values of out_M 
                                  with 'val' - for instance '0'
          out_M(k,2) = out_M(k,2)-out_M(1,2); // Till the first column 
                                                 values are zero in 
                                                 out_M, I want to do this
                                                 subtraction.
          end
     end

Hope now its a bit clearer.. Sorry to cause confusion..

Pramit end

[Adam Wyatt]

Your problem still does not make sense - M(:, 1) is always zero, so the case statement will only occur for j=1, and for all M(:, 1).

The statement "// Till the first column values are zero in out_M, I want to do this subtraction" doesn't make sense (neglecting the incorrect comment symbol). Do you want to do the subtraction until M(k, 1)~=val and then move on to the next j? then use if out_M(k,1)~=val; continue; else; out_M(k, 2) = ...; end

[pramit Sood]

Ya you are right!! It would only occur for j=1 but the if statement should do the subtraction atleast 107 times when first column of out_M is '0'. It is doing the subtraction only once... :(

Regards

Pramit

Answer 2

[Adam Wyatt]

• Your code could easily be vectorized.
• never use i or j for indexing because these are used for sqrt(-1) and can easily cause bugs. I would use nR and nM so that it is clear that these indices refer to the loop over the R position and M position.
• You don't need to enter a step size of 1 (i.e. 1:11 is the same as 1:1:11)

Anyway, out_M(:, 1) always equals 0, so the contents of the case statement is not executed except when out_R==0 (i.e. the first j iteration). Also, M(1,2)==0, so that statement doesn't actually change any values!!

I would do the following (1 loop)

for nR=1:length(out_R)
	test = (out_M(:, 1) == out_R(nR));
	out_M(test, 2) = out_M(test, 2) - out_M(1, 2);
end

[pramit Sood]

Hi Adam! Thank you for your info notes.. :) Well the code also kind of works.. Thank you!! :)

But my original out_M matrix is what is attached here.. So as you see there are cycles of 0's, 1's ,2's and so on goes on uptil the end value of out_R that is 10.

Like I subtracted the first value of the second column i.e-out_M(1,2) from all the other values in out_M(:,2) for 0's cycle, I want to ask is it somehow possible if I can subtract the first value of 1's, 2's or 3's cycle from all the other values in the second column for that particular cycle..

I know it is confusing to explain.. for example- for 0's cycle - I subtract 55.752 for 1's cycle - I subtract 116.03 (from where the 1's cycle start) for 2's cycle - I subtract 176.294 (from where the 2's cycle start)

and so on..

I look forward to your suggestion..

Regards

Pramit

Answer 3

[Andrei Bobrov]

ii = ismember(out_M(:,1),out_R);
out_M(ii,2) = out_M(ii,2) - out_M(1,2);

?