Example 1: Cayley-Hamilton theorem. Consider the matrix. A = 1, 1. 2, 1. Its characteristic polynomial is. p() = det (A – I) = 1 -, 1, = (1 -)2 – 2 = 2 – 2 – 1. 2, 1 -. Cayley-Hamilton Examples. The Cayley Hamilton Theorem states that a square n × n matrix A satisfies its own characteristic equation. Thus, we. In linear algebra, the Cayley–Hamilton theorem states that every square matrix over a As a concrete example, let. A = (1 2 3 .. 1 + x2, and B3(x1, x2, x3) = x 3.

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There is no such matrix representation for the octonionssince the multiplication operation is not associative in this case.

### Cayley–Hamilton theorem – Wikipedia

While this provides a valid proof, the argument is not very satisfactory, since the identities represented by the theorem do not in any way depend on the nature of the matrix diagonalizable or notnor on the kind of entries allowed for matrices with real entries the diagonalizable ones do not form a dense set, and it seems strange one would have to consider complex matrices to see that the Cayley—Hamilton theorem holds for them.

Enter your email address to subscribe to this blog and receive notifications of new posts by email. So when considering polynomials in t with matrix coefficients, the variable t must not be thought of as an “unknown”, but as a formal symbol that is to be manipulated according to given rules; in particular one cannot just set t to a specific value. But this map is not a ring homomorphism: The theorem was first proved in [8] in terms of inverses of linear functions of quaternionsa non-commutative ring, by Hamilton.

Writing these equations then for i from n down to 0, one finds. A is just a scalar.

As indicated, the Cayley—Hamilton theorem amounts to the identity. This requires considerable care, since it is somewhat unusual to consider polynomials with coefficients in a non-commutative ring, and not all reasoning that is valid for commutative polynomials can be applied in this setting.

Views Read Edit View history. Theorems in linear algebra Matrix theory William Rowan Hamilton. Read solution Click here if solved Add to solve later. But, in this commutative setting, it is valid to set t to A in the equation.

Read solution Click here if solved 51 Add to solve later. This proof is similar to the first one, but tries to give meaning to the notion of polynomial with matrix coefficients that was suggested by the expressions occurring in that proof.

Now viewed as theodem function e: But this statement is demonstrably wrong. Thus, it follows that. At this point, it is tempting to simply set t equal to the matrix Awhich makes the first factor on the left equal to the null matrix, and the right hand caylry equal to p A ; however, this is not an allowed operation when coefficients do not commute.

When the ring is a field, the Cayley—Hamilton theorem is equivalent to the statement that the minimal polynomial of a square matrix divides its characteristic polynomial. The list of linear algebra problems is available here. Note, caylej, that if scalar multiples of identity matrices instead of scalars hamlton subtracted in the above, i.

Thus, the determinant can be written as a trace identity. In linear algebrathe Cayley—Hamilton theorem named after the mathematicians Arthur Cayley and William Rowan Hamilton states that every square matrix over a commutative ring such as the real or complex field satisfies its own characteristic equation. Thus, there are the extra m — 1 linearly independent solutions.

For any fixed value of n these identities can be obtained by tedious but completely straightforward algebraic manipulations. It is possible to define a “right-evaluation map” ev A: One can work around this difficulty in the particular situation at hand, since the above right-evaluation map does become a ring homomorphism if the matrix A is in the center of the ring of coefficients, 3s3 that it commutes with all the coefficients of the polynomials the argument proving this is straightforward, exactly because commuting t with coefficients is now justified after evaluation.

Now if A admits a basis of eigenvectors, in other words if A is diagonalizablethen the Cayley—Hamilton theorem must hold for Asince two matrices that give 3x same values when applied to each element of a basis must be equal.

To illustrate, consider the characteristic polynomial in the previous example again:. They vary in the amount of abstract algebraic notions required to understand the proof. Thus, exa,ple can express c i in terms of the trace of powers of A.

If so, prove it. Retrieved from ” https: In fact, matrix power of any order k can be written as a matrix polynomial of degree at most n – 1where n is the size of a square matrix.

Therefore, the Euclidean division examplf in fact be performed within that commutative polynomial ring, and of course it then gives the same quotient B and remainder 0 as in the larger ring; in particular this shows that B in fact lies in R [ A ] [ t ].

Indeed, even over a non-commutative ring, Euclidean division by a monic polynomial P is defined, and always produces a unique quotient and remainder with the same degree condition as in the commutative case, provided it is specified at which side one wishes P to be a factor here that is to the left. From Wikipedia, the free encyclopedia. This is important to note here, because these relations will be applied below for matrices with non-numeric entries such exxmple polynomials.

If not, give a counter example. Since B is also a matrix with polynomials in t as entries, one can, for each icollect the coefficients of t i in each entry to form a matrix B i of numbers, such that one has. When restricted to unit norm, these are the groups SU 2 and SU 1, 1 respectively. Read solution Click here if solved 45 Add to solve later.

However, the right hand side of the above equation is the value of a determinant, which is a scalar. Again, this requires a ring containing the rational numbers. In addition to proving the theorem, the above argument tells us that the coefficients B i of B are polynomials in Awhile from the second proof we only knew that they lie in the centralizer Z of A ; in general Z is a larger subring than R [ A ]and not necessarily commutative.

Read solution Click here if solved 9 Add to solve later. This proof uses just the kind of objects needed to formulate the Cayley—Hamilton theorem: It is apparent from the general formula for c n-kexpressed in terms of Bell polynomials, that the expressions.

We shall therefore now consider only arguments that prove the theorem directly for any matrix using algebraic manipulations only; these also have the benefit of working for matrices with entries in any commutative ring. In particular, the determinant of A corresponds to c 0. However, since End V is not a commutative ring, no determinant is defined on M nEnd V ; this can only be done for matrices over a commutative subring of End V.

Finally, multiply the equation of the coefficients of t i from the left by A iand sum up:.

## Cayley–Hamilton Theorem

Compute the Determinant of a Magic Square. The coefficients c i are given by the elementary symmetric polynomials of the eigenvalues of A. There is thdorem great variety of such proofs of the Cayley—Hamilton theorem, of which several will be given here.