Reversible matrix in matlab

2020 10 20
2 个回答
更新时间：2020 10 21
10 次查看（30 天）

0 个投票

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?

7 个评论
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Walter Roberson
Walter Roberson 2020-10-20
What filename did you store the code in?
Walter Roberson
Walter Roberson 2020-10-20
p is not defined in your function by the way.
Noa Yelin
Noa Yelin 2020-10-20
I don't understand...
KSSV
KSSV 2020-10-20
What do you mean by a matrix is reversible?
Noa Yelin
Noa Yelin 2020-10-20
Regular matrix and non-singular matrix
KSSV
KSSV 2020-10-20
What is sz in the function? It will throw error.
Noa Yelin
Noa Yelin 2020-10-20
this is how I create array of 0

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回答（2 个）

Walter Roberson
Walter Roberson 2020-10-20

1 个投票

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

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Noa Yelin
Noa Yelin 2020-10-20
how i do this?
Walter Roberson
Walter Roberson 2020-10-20
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
Noa Yelin 2020-10-20
i did this, and than get this note -
Error in Untitled5 (line 2)
irr_mat(A)
Noa Yelin
Noa Yelin 2020-10-20
any help please?
Jan
Jan 2020-10-20
Please post the complete error message.
Noa Yelin
Noa Yelin 2020-10-20
Error in irr_mat (line 3)
if A==zeros(n)
Error in Untitled5 (line 3)
irr_mat(A)
Walter Roberson
Walter Roberson 2020-10-20
编辑：Walter Roberson 2020-10-20
What is n in the code?
Also change the test to
if isequal(A,zeros(n))
Noa Yelin
Noa Yelin 2020-10-20
n is the array of matrix
Noa Yelin
Noa Yelin 2020-10-20
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
Noa Yelin 2020-10-20
n is the array of matrix
Steven Lord
Steven Lord 2020-10-20
You asked a continuation question here. In the future, please keep discussions of the same issue in one Answers post.
Noa Yelin
Noa Yelin 2020-10-20
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)

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Jan
Jan 2020-10-20
编辑：Jan 2020-10-21

0 个投票

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.

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Noa Yelin
Noa Yelin 2020-10-20
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
Noa Yelin 2020-10-20
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
Noa Yelin 2020-10-20
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
Walter Roberson 2020-10-20
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
Jan 2020-10-21
@Noa Yelin: I had a bug in the code, which is fixed now. See my answer.

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Noa Yelin
Noa Yelin
2020-10-20

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2020-10-21

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