How to define a polynomial which can take matrix ?

daviddgl
55 ●4 ●4 ●11

tmonteil
27483 ●32 ●205 ●519 http://wiki.sagemath.o...

I want to define a matrix valued function. for example..

If I have a polynomial of a matrix with me say $f(x)$ and I want to check $f(A)$ . What can be done better? The following will work for numbers but not for matrix.

var('x')
f(x)=2x^2+x+3 
print f(A)# this is what I want as an answer..

In the above if I want to replace my x by a matrix what I have to do?

So, ultimate aim is to find define a polynomial which can take matrix Thanks in advance...

answered 8 years ago

tmonteil
27483 ●32 ●205 ●519 http://wiki.sagemath.o...

You should work with polynomials, not symbolic expressions.

Here is an example, let us assume that your matrix is defined over the field QQ:

sage: A = random_matrix(QQ,3)
sage: A
[   2    0   -2]
[   2    2    0]
[-1/2    0    0]

Then you can define the polynomial ring with one variable over the rationals, and define your polynomial:

sage: R.<x> = PolynomialRing(QQ)
sage: R
Univariate Polynomial Ring in x over Rational Field
sage: f = 2*x^2 + x + 3
sage: f.parent()
Univariate Polynomial Ring in x over Rational Field

And apply it to your matrix:

sage: f(A)
[  15    0  -10]
[  18   13   -8]
[-5/2    0    5]

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Thank you so much..

daviddgl ( 8 years ago )

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How to define a polynomial which can take matrix ?

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In the above if I want to replace my x by a matrix what I have to do?

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