i want to find the max element in each row and position of that element in terms of row and column

i am giving the example what i have tried and what result i have got

 c=  2     3     4     5
    67    58    79    81
    91    23    56    78
[max_num,max_idx]=max(c,[],2)

 max_num =

     5
    81
    91
 max_idx =

     4
     4
     1

 >> [X,Y]=ind2sub(size(c),max_idx)

 X =

     1
     1
     1

 Y =

     2
     2
     1

i am not getting the right ans in first row max element is 5 postion will be (1,4)

Answer 1

[Image Analyst]

You made a common novice user mistake: mistaking (row, column) for (x, y). Note: row is Y, not X. and column is X, not Y. ind2sub() returns [row, column], NOT [X, Y]. So you might be tempted to do:

[Y, X] = ind2sub(size(c), max_idx)

however even that is not right. Why not? Because max_idx is not the linear index over the whole matrix - it is the column number of each row. For example while max() might give [4,4,1], the linear indexes would be [4,8,9]. But that is not what you were passing in to ind2sub, you were passing in [4,4,1], so it didn't give you the expected output.

To correct the code, see the solution Star Strider gave you.

[praveen rai]

good xplanation didnt get this line'see the solution Star Strider gave you'.

[praveen rai]

sorry i got what it means 'see the solution Star Strider gave you'.thnx

Answer 2

[Star Strider]

The max function is returning the column numbers of the maximum in each row, because you asked it to. If you want to return the row and column of the row maxima, you have to provide the row indices:

rc_max = [(1:size(c,1))' max_idx]

rc_max =
     1     4
     2     4
     3     1

That should be the result you want.

[praveen rai]

thnx and ur line of code is working can u explain the single inverted comma u put in code what does that mean??

[Walter Roberson]

See https://www.mathworks.com/help/matlab/ref/ctranspose.html

Answer 3

[Walter Roberson]

X = 1:size(c, 1)
Y = max_idx