Printing Results out of a for Loop

I have Written a Small Function that Returns the Absolute Difference Between the Max and Min Elements of Each Row in a Matrix and Assigns the Results to the output "rows_diff" as Row Vector and Also Gets the Diff. Between the Max and Min of Whole Matrix in "tot_diff"

All what I want to Know is How to Print Out the Results of the for Loop Returning them in "rows_diff" as row vector not just the Last Result as the Case with this Version of the Function:-

function [rows_diff, tot_diff] = minimax(M)

a = size(M,1);

for i = 1:a

rows_diff = abs(max(M(i,:)) - min(M(i,:)));

end

tot_diff = max(M(:)) - min(M(:));

[Stephen23]

Note that avoiding the loop gives simpler, more efficient code:

>> M = magic(5) % fake data.
M =
   17   24    1    8   15
   23    5    7   14   16
    4    6   13   20   22
   10   12   19   21    3
   11   18   25    2    9
>> minimax(M) % function with loop (following Ruger28's bugfix).
ans =
   23   18   18   18   23
>> max(M,[],2) - min(M,[],2) % no loop required, more efficient.
ans =
   23
   18
   18
   18
   23

[Ammar Taha]

Thanks Again Stephen, but I was doing an Assigment for a Course and it was Required to use for Loop Specificaly.

I have read this before and I will try to Aviod Looping in Future.

Answer 1

[Ruger28]

rows_diff = abs(max(M(i,:)) - min(M(i,:)));

This overwrites the value of rows_diff each time. This is ok if you just want to print it out, but to store it (which seems like you want to) you need:

rows_diff(i) = abs(max(M(i,:)) - min(M(i,:)));

to print this value, in your loop place a fprintf

fprintf('Value of rows_diff = %f\n',rows_diff(i))

[Stephen23]

Remember to preallocate any arrays before the loop:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

[Ammar Taha]

Thanks alot Stephen Matlab has Pointed this Out and I Made it :)

Answer 2

[Alex Mcaulley]

You can also implement the function in a simpler and efficient way:

function [rows_diff, tot_diff] = minimax(M)
    rows_diff = arrayfun(@(i) abs(max(M(i,:)) - min(M(i,:))),1:size(M,1))';
    tot_diff = max(M(:)) - min(M(:));
end

[Stephen23]

"You can also implement the function in a simpler and efficient way:"

arrayfun is unlikely to be an efficient approach (1e5 iterations, 12x12 matrix):

Elapsed time is 8.715833 seconds.  % Ruger28's bugfix (no preallocation).
Elapsed time is 6.902387 seconds.  % Ruger28's bugfix (preallcoated).
Elapsed time is 21.641814 seconds. % your ARRAYFUN solution.
Elapsed time is 0.597622 seconds.  % my solution without a loop.

[Ammar Taha]

Thanks Alex Mcaulley this is efficient and neat :)

[Ammar Taha]

I have got Benefits from your solution Stephen Cobeldick it Forced me to Review the Format of (max), but as I said it was required to Use Loops

But at all Thank you for your Attention :)

Answer 3

[Ammar Taha]

Thank you Ruger28 it Worked :)

[Ruger28]

no problem, glad to be of some help.