get the minimum and maximum element from two vectors.

Hi.

That is question.

Write a MATLAB function called minMaxVectors that takes two vectors v1 and v2 (you can assume these vectors have the same length) as its parameters and returns two values: the minimum of both of these vectors, and the maximum of both of these vectors. You must also write a driver file called minMaxVectorsDriver to test your program.

Testing

Your driver program should embed test cases and print the results returned by minMaxVectors. Some example test cases are:

input1 input 2 min max

[ 1 2 ] [ 3 4 ] 1 4

[ 5 ] [ -5 ] -5 5

[ 1 9 ] [ 5 6 ] 1 9

That is my code

% That is function file

function [d1 d2] = minMaxVectors(v1,v2)

n1 = 0;

n2 = 0;

for i = 1:length(v1)

if n1 > v1(i) % if the number of min is bigger than v1

n1 = v1(i); % let min is equal to the elements of v1

d1 = n1;

end

end

for i = 1:length(v2)

if n2 < v2(i) % if the number of min is smaller than v2

n2 = v2(i); % let max is equal to the elements of v2

d2 = n2;

end

end

if n1 < n2

d1 = n1;

end

end

That is test file

% set two vector, first vector elements are 1 4,

% second vector elements are 4 -1

v1 = [1 4];

v2 = [4 -1];

[num1 num2] = minMaxVectors(v1,v2);

disp([num1 num2]);

On my code, it cannot be get the minimum element by comparing two vectors

The output is 0 4

How to improve my code?

Thank you all.

Answer 1

[Davide Masiello]

You could use the min and max MatLab inbuilt functions.

v1 = [1 4];
v2 = [4 -1];
[num1 num2] = minMaxVectors(v1,v2);
disp([num1 num2])

    -1     4

function [minval maxval] = minMaxVectors(v1,v2)
minval = min([v1,v2]);
maxval = max([v1,v2]);
end

[Shuoze Xu]

cool, thank you.

Answer 2

[Riccardo Scorretti]

Dear Shouze, as your question looks like an assignment I'll provide only some hints, but I will not write any code in your place; I'm sure you will understand.

1. To begin with, your algorithm has a weak point: you initializes n1 = n2 = 0. This is an error, which is likely to produce a wrong result: you should initialize them as n1 = inf and n2 = -inf if you want to obtain the correct result.
2. Concerning names, when you read a program you must be able to tell which is the meaning of each variable (as much as possible, of course). In your case, the names n1 and n2 are meaningless: try to use something like minval instead of n1, and maxval instead of n2: your program will be much more readable.
3. You could initialise n1 = n2 = v1(1) and start the first loop (and the first only!) from i = 2.
4. Never use i and j as names of variables: it may be confounded with the imaginary unit 1i - expecially if you program in Matlab. Avoid also the variable l (= "letter L") because it can be easily misread as 1 (= "one") or | (= "or operator").
5. You don't need the variables d1 and d2: just use n1 and n2.
6. Last but not least, you wrote an algorithm in "C-style". In Matlab it would be much more effective to create a matrix the columns of which are the two vectors v1 and v2 (for instance by using mat = [v1(:) v2(:)]; the symbols (:) are required to ensure that v1(:) and v2(:) are column-vectors) then use the functions min and max (read the doc to know how).

[Shuoze Xu]

Wow, i will do that.

May you tell me what is the meaning of n1 = inf?

[Riccardo Scorretti]

Sure. inf = infinity. In your code, n1 = best candidate for the minimum. At the beginning of your algorithm, you should

• either initialize n1 with v1(1) (assuming that v1 is not empty, otherwise you'll get an error) because min(v1) <= v1(1),
• or n1 = inf because of course min(v1) <= inf.

If you initialize n1 = 0, you are implicitly assuming that min(v1) <= 0, which is likely to be wrong, and hence it will produce a wrong result. Even if you have specific a priori information on your data (= you are sure that min(v1) < 0), this is an extremely bad programming practice, and should be avoided in any case.

[Shuoze Xu]

I understand, and i have done that by using for loop.

Thanks for your help.