find max of vector

i want to find the maximum of a vector and its position, if i have for example v=[-1,3,4,5,-2,5] , the max is 5 but i have two positions , how can i find these two positions using for loops , here is my program but it doesn't work :

v=[-1,3,4,5,-2,5]
maxi=v(1);
j=1;
for i=2:length(v)
    if v(i)>maxi
        maxi=v(i);
        pos(j)=i; 
        j=j+1;
    end
   
end

Answer 1

[the cyclist]

m = max(v);
idx = find(v==m);

[diadalina]

thank you mr cyclist for your answer, but i want the loops for way

Answer 2

[James Tursa]

Two things. FIrst, you need to initialize pos = 1 before the loop starts. And second, you need to modify your if-test to do two things: If v(i) == maxi, then add another pos(j) similar to what you are currently doing, but if v(i) > maxi then you need to start over and save a new max. Currently you keep adding in new pos(j) values when a new max is found but not getting rid of the old ones. E.g.,

if v(i) == maxi
        j=j+1;
        pos(j)=i; 
elseif v(i) > maxi
    % code to save new max value in maxi, and start over with pos = i etc.
end

I will leave it to you to fill in the missing code.

[diadalina]

do you mean like this, bit still doesn't give me the two positions: v=[-1,3,4,5,-2,5]

maxi=v(1);

j=1;

for i=2:length(v)

if v(i) == maxi

maxi=v(i);

pos(j)=i;

j=j+1;

else if v(i)>maxi

pos(j) = i;

maxi=v(i);

end

end

[James Tursa]

   else if v(i)>maxi
 pos(j) = i; 

No. Here you are just adding another index to the pos(j) spot. You need to overwrite all of those stored pos values and start over your index saving completely:

 pos = i;
 j = 1;

Also, remember you need to initialize your pos vector prior to the start of the loop:

 pos = 1;

Finally, I suggest you use the code I gave you for the condition of v(i) == maxi

[diadalina]

v=[-1,3,4,5,-2,5]

maxi=v(1);

j=1;;

pos=1;

for i=2:length(v)

for j= 1:length(v)

if v(i) == maxi

maxi=v(i);

pos(j)=i;

else if v(i)>maxi

pos = i;

maxi=v(i);

j=1;

end

end

end

end

it doesn't work alsopos =

6 6 6 6 6 6

maxi =

5

[James Tursa]

We seem to be diverging here, and you are not implementing my advice. For example, now you have two for-loops:

for i=2:length(v)
    for j= 1:length(v)

Why are you suddenly introducing an additional for-loop?

And you still haven't implemented the code I gave you for the v(i) == maxi case.