# Reversible matrix in matlab

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Noa Yelin on 20 Oct 2020
Commented: Jan on 21 Oct 2020
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)

Noa Yelin on 20 Oct 2020
Regular matrix and non-singular matrix
KSSV on 20 Oct 2020
What is sz in the function? It will throw error.
Noa Yelin on 20 Oct 2020
this is how I create array of 0

Walter Roberson on 20 Oct 2020
You need to take that code for irr_mat and store it in file irr_mat.m

Noa Yelin on 20 Oct 2020
any help?
Steven Lord on 20 Oct 2020
You asked a continuation question here. In the future, please keep discussions of the same issue in one Answers post.
Noa Yelin on 20 Oct 2020
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)

Jan on 20 Oct 2020
Edited: Jan on 21 Oct 2020
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 on 20 Oct 2020
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 on 20 Oct 2020
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 on 21 Oct 2020
@Noa Yelin: I had a bug in the code, which is fixed now. See my answer.