Finding the maximum of rows

Say that we have the following matrix:

I=[3 4; 5 3; 6 3; 7 4];

If we want to find the maximum value in each row, we can do the following:

m=max(I,[],2);

For m, how do we read this? How is the statement interpreted? What should we do if we want to find the maxim of the columns?

Thanks.

[Jonathan Timberlake]

HI how would you take the max of every other row?

[Wesley Brigner]

There are probably multiple ways to find the max of every other row, but the simplest I can think of is to just use matrix indexing:

i=1;                        % Changes the starting row.  Can be either 1 or 2.
m=max(I(i:2:end,:),[],2);

Of course, this can be generalized if you want to take every nth row:

i=1;                        % Changes the starting row.  Positive integer between 1 and n.
n=4;                        % Changes the increment.  Positive integer.
m=max(I(i:n:end,:),[],2);

Answer 1

[Wayne King]

 [m,idx] = max(I,[],2);

m gives you the maximum value in each row and idx gives you the column in which it occurs. I used this in my other response to you about fcm()

To find the maximum of the columns, just operate along the rows

 [m,idx] = max(I,[],1);

[med-sweng]

Thanks for your reply. What does [] represent here?

[Wayne King]

Are you reading the documentation?? The syntax max(x,y) takes the maximum of x or y, so if you just called:

max(I,1)

that would not give you what you want. You want 1 or 2 to represent the dimension along which you want the maximum and that has to be the third input argument.

[Walter Roberson]

max(A) means the maximum of A column-wise

max(A,B) means the maximum element-by-element of A(I,J) vs B(I,J)

max(A,[],k) means the maximum of A along the k'th dimension. You need the [] as a place-holder so that MATLAB does not confuse this with max(A,B)

Answer 2

[Ariunbolor Purvee]

clc;clear

absDiff=[1 2 3; 4 5 6; 7 8 9; 9 10 12];

MaxMinAveRow= MaxMinAveOfRow(absDiff);

display(MaxMinAveRow);

function MaxMinAveRow= MaxMinAveOfRow(absDiff)

n=length(absDiff);

maxRow=zeros(n,1);

minRow=zeros(n,1);

aveRow=zeros(n,1);

sum=0;

for i=1:n

maxRow(i)=sum+max(absDiff(i,:));% max of row

minRow(i)=sum+min(absDiff(i,:));% min of row

aveRow(i)=sum+mean(absDiff(i,:));% average of row

end

MaxMinAveRow=[ maxRow,minRow, aveRow ];

end

Result on Command Window

MaxMinAveRow =

3.0000 1.0000 2.0000

6.0000 4.0000 5.0000

9.0000 7.0000 8.0000

12.0000 9.0000 10.3333