Find min and max value of vector without using built-in function

Hello, I know that this question has been already asked many times, however, I kind of struggle to execute it. Max shows correct result, but the not the minimum value. What could be the solution?

A = [9  6  8  3 6 8 2 1 3 9 1 0 2]
maxval = A(1);
minval = 1;
for i = 1:length(A)
    if A(i) > maxval
        maxval = A(i);
    else A(i) < minval
        minval = A(i)
    end
end

Answer 1

[dpb]

...
minval=maxval;
...
if ...
  ...
elseif A(i) < minval            %%% HERE'S YOUR PROBLEM...SEE IT???
  ...  

You missed the "if" part on the "else" clause -- so every thing that wasn't greater than went there and the {A(i) < minval) clause did nothing except display the result of the test to the command line; had no bearing on the logic.

[Matt J]

Note that this implementation is not robust to the case where A(1)=nan,

A = [nan  6  8  3 6 8 2 1 3 9 1 0 2];
maxval = A(1);
minval = maxval;
for i = 1:length(A)
    if A(i) > maxval
        maxval = A(i);
    elseif A(i) < minval
        minval = A(i);
    end
end

minval,maxval

minval = NaN

maxval = NaN

whereas minval=inf, maxval=inf will work.

[dpb]

True...but the else instead of elseif doesn't work at all...

[Voss]

The if/elseif should really be two independent ifs if initializing with Infs:

A = 1:10; % strictly increasing -> elseif condition never checked
maxval = -Inf;
minval = Inf;
for i = 1:length(A)
    if A(i) > maxval
        maxval = A(i);
    elseif A(i) < minval
        minval = A(i);
    end
end

minval,maxval % minval remains Inf

minval = Inf

maxval = 10

A = 1:10;
maxval = -Inf;
minval = Inf;
for i = 1:length(A)
    if A(i) > maxval
        maxval = A(i);
    end
    if A(i) < minval
        minval = A(i);
    end
end

minval,maxval

minval = 1

maxval = 10

[Dan Kristen]

Thank you so much!

Answer 2

[Matt J]

%maxval = A(1);
%minval = 1;
maxval = -inf;
minval = +inf;