Reversible matrix in matlab

Hey

I need to write a function that the user enters a matrix, and the function returns "1" if the matrix is reversible and "0" if it's not.

I wrote this function-

function x=irr_mat(A)
if A==zeros(sz,'like',p)
    x=0;
else
   if size(A,1)==size(A,2)
    x=1;
else
    x=0;
   end
end
end

and when I call the function-

A=randi([1,100],4);
irr_mat(A)

I get a note that -

Undefined function 'irr_mat' for input arguments of type 'double'.

Error in Untitled5 (line 3)
irr_mat(A)

can someone help me please?

[Walter Roberson]

What filename did you store the code in?

[Walter Roberson]

p is not defined in your function by the way.

[Noa Yelin]

I don't understand...

[KSSV]

What do you mean by a matrix is reversible?

[Noa Yelin]

Regular matrix and non-singular matrix

[KSSV]

What is sz in the function? It will throw error.

[Noa Yelin]

this is how I create array of 0

Answer 1

[Walter Roberson]

You need to take that code for irr_mat and store it in file irr_mat.m

[Noa Yelin]

how i do this?

[Walter Roberson]

At the MATLAB command line give the command

edit irr_mat

The editor will open. In the page it creates, copy out that function code you posted, and paste it into the editor session. Now click on the menu entry to save the file.

[Noa Yelin]

i did this, and than get this note -

Error in Untitled5 (line 2)
irr_mat(A)

[Noa Yelin]

any help please?

[Jan]

Please post the complete error message.

[Noa Yelin]

Error in irr_mat (line 3)
if A==zeros(n)

Error in Untitled5 (line 3)
irr_mat(A)

[Walter Roberson]

What is n in the code?

Also change the test to

if isequal(A,zeros(n))

[Noa Yelin]

n is the array of matrix

[Noa Yelin]

it doesn't work with this -

if isequal(A,zeros(n))

i got this note -

Error in irr_mat (line 3)
if isequal(A,zeros(n))

Error in Untitled5 (line 3)
irr_mat(A)

[Noa Yelin]

n is the array of matrix

[Noa Yelin]

any help?

[Steven Lord]

You asked a continuation question here. In the future, please keep discussions of the same issue in one Answers post.

[Noa Yelin]

of this is right??

function x=irr_mat(A)
n=size(A)
if isequal(A,zeros(n))
    x=0;
else
   if size(A,1)==size(A,2)
    x=1;
else
    x=0;
   end
end
end

and I call the function -

A=randi([6,100],2,2);
irr_mat(A)

Answer 2

[Jan]

You want to identify a "regular matrix and non-singular matrix". Then testing only, if it is square and not a zero matrix ist not sufficient. Even matrices with non-zero elements can be singular.

It is hard to guess, if your code is "correct", because you do not explain what you try to achieve. Therefore just some hints:

n=size(A)
if isequal(A,zeros(n))

is equivalent to:

if any(A)    

So your code canbe simplified to:

function x = irr_mat(A)
if any(A(:)) && size(A, 1) == size(A, 2) && ismatrix(A)  % BUGFIX: any(A) -> any(A(:))
    x = 1;
else
    x = 0;
end
end

% Or shorter:
function x = irr_mat(A)
x = (any(A) && size(A, 1) == size(A, 2) && ismatrix(A));
end

But this is not a hard test for singularity.

[Noa Yelin]

Invertible matrix-

In linear algebra, an n-by-n square matrix A is called invertible (also nonsingular or nondegenerate), if there exists an n-by-n square matrix B such that A B = B A = I n {\displaystyle \mathbf {AB} =\mathbf {BA} =\mathbf {I} _{n}\ }

where In denotes the n-by-n identity matrix and the multiplication used is ordinary matrix multiplication. If this is the case, then the matrix B is uniquely determined by A, and is called the (multiplicative) inverse of A, denoted by A−1.[1][2] Matrix inversion is the process of finding the matrix B that satisfies the prior equation for a given invertible matrix A.

I need to write a function that the user enters a matrix, and the function returns "1" if the matrix is reversible and "0" if it's not.

[Noa Yelin]

and that code -

function x = irr_mat(A)
if any(A) && size(A, 1) == size(A, 2) && ismatrix(A)
    x = 1;
else
    x = 0;
end
end

doesn't work.. this note -

Error in shortmat (line 2)
if any(A) && size(A, 1) == size(A, 2) && ismatrix(A)

[Noa Yelin]

now i have changed the code to this -

function x=withdet(b)
if det(b)~=0 && size(b,1)==size(b,2)
    x=1;
else
    x=0;
end
end

and it works only when i call to function with one number -

b=randi([0,12],4);
withdet(b)

but when I call to the function like this -

b=randi([0,12],4,8);
withdet(b)

i get this note -

Error in withdet (line 2)
if det(b)~=0 && size(b,1)==size(b,2)

Error in Untitled9 (line 3)
withdet(b)

[Walter Roberson]

You need to post complete error messages indicating what the error is, not just where it is. For example is it complaining that there is no such function det for inputs of class DynamicSystem ?

Reminder: det() will generate an error if it is passed something that is not a square matrix, so you should never call det() until after you have ensure that the matrix is square.

[Jan]

@Noa Yelin: I had a bug in the code, which is fixed now. See my answer.