progrem witch sort matrix from user

hey guys

i have a big problem here

i need to write a progrem witch get matrix from user non stop until he writes "0" (not as part of the matrix , only the num "0"

after i get the matrix's i need to sort them by there sum in acending order (the first mat the user wrote will be the one with the smallest sum )

for somereason nothing worked ive been working on it for 6 hours in diffirnent ways and manage to do harder thing

please help me

thx

[James Tursa]

Please post the code you are currently using and explain the specific problems you are having. Then we can help fix up your code.

[shay shemesh]

first im trying to get the matrix from user

im trying to use a cell array but for some reason its wont work

i=1

while mat{i} ==0

mat{i} = input('Please input matrix ')

end

i get the error

Undefined variable mat.

Error in untitled3 (line 3)

while mat{i} ==0

[Rik]

You're trying to test it it is zero before it is created. You need to create mat{i} first.

[shay shemesh]

ok so i kept going with it , its worked a couple of times , and then suddnly stoped affter 2 matrix input

im trying to sum up all the matrix after input them

then i will sort it

%% Q3

i=1;

mat{1} = input('Please input matrix ');

s(1)=sum(mat{1},'all');

while mat{i} ~= [0];

mat{i+1} = input('Please input matrix ');

s(i+1)=sum(mat{i},'all');

i=i+1;

end

Answer 1

[Jan]

k     = 1;    % Avoid "i" to reduce confusions with the imaginary unit
ready = false;
mat   = {};
while ~ready
   mat{k} = input('Please input matrix ');
   ready  = isequal(mat{k}, 0);  % Check if input is 0
   k      = k + 1;
end

An alternative ís an infinite loop and a break command:

k   = 0;
mat = {};
while true  % Infinite loop
   data = input('Please input matrix ');
   if isequal(data, 0)
      break;  % Jump behind the loop
   end
   k      = k + 1;
   mat{k} = data;
end

[shay shemesh]

ok so i kept going with it , its worked a couple of times , and then suddnly stoped affter 2 matrix input

im trying to sum up all the matrix after input them

then i will sort it

%% Q3

i=1;

mat{1} = input('Please input matrix ');

s(1)=sum(mat{1},'all');

while mat{i} ~= [0];

mat{i+1} = input('Please input matrix ');

s(i+1)=sum(mat{i},'all');

i=i+1;

end

[Jan]

I've posted two examples containing isequal(mat{i}, 0). It is a good idea to consider such suggestions. The comparison mat{i} ~= [0] does something else. while and if comnmands require a scalar condition. If you compare a matrix with a scalar, the comparison is done elementwise:

x = rand(2,3);
x == 0

This is a 2x3 matrix. If this is used as condition, Matlab inserts an all() automatically:

while all(mat{i} ~= 0, 'all')

This stops, if any element of mat{i} is zero, while isequal(mat{i}, 0) tests, if the matrix is a scalar 0.

By the way: [] is Matlab's operator for concatenation. [0] concatenates 0 with nothing, so the square brackets are a waste of time only.

The trailing semicolon ; suppresses the output. A while command does not have an output, so it is nicer to omit the semicolon here.

This line:

mat{i+1} = input('Please input matrix ');    

appears twice in your code. It is working, but such "code duplications" are a source of bugs, when the code is growing: it happens too frequently, that one of the lines is modified, but the other is not. Therefore it is a good programming practice to avoid duplicate code. See the examples in my answer.