ASKSAGE: Sage Q&A Forum - Latest question feedhttp://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Fri, 10 Jan 2020 16:05:24 -0600Eigenvalues and eigenspaces of orthogonal (or rotation) matriceshttp://ask.sagemath.org/question/49496/eigenvalues-and-eigenspaces-of-orthogonal-or-rotation-matrices/Given an orthogonal transformation of finite order, e.g.
Matrix([[0,0,0,-1],[1,0,0,-1],[0,1,0,-1],[0,0,1,-1]])
Its eigenvalues are going to be of the form
exp(I*pi/5),exp(2*I*pi/5),...,exp(2*I*pi*m),...
corresponding to a splitting of the matrix into rotation (and reflection) matrices. I'd like to extract these fractions `m` (mod ZZ) and study the corresponding (real rotation and reflection) eigenspaces.
My impression is that Sage isn't suitable for doing this directly, but that I should use e.g. the Maxima or Mathematica interface? Any suggestions for the most suitable method?Bob67846Fri, 10 Jan 2020 16:05:24 -0600http://ask.sagemath.org/question/49496/Is there any way to find the eigenvalues of a matrix in terms of a variable?http://ask.sagemath.org/question/49488/is-there-any-way-to-find-the-eigenvalues-of-a-matrix-in-terms-of-a-variable/ I have the following matrix
M=
2n-1 & n-1 & n
1 & 2n-3 & 0
1& 0 & 1
Here $n$ is a variable
I want to find its eigenvalues.
Is there any way to find the eigenvalues of this matrix in terms of $n$ in sagemath.
I even cant input a matrix in terms of a variable.
Can someone please help me out?CaptchaFri, 10 Jan 2020 04:36:02 -0600http://ask.sagemath.org/question/49488/Pairs of graphs with same spectral radius but with different diameter and different number of edgeshttp://ask.sagemath.org/question/41990/pairs-of-graphs-with-same-spectral-radius-but-with-different-diameter-and-different-number-of-edges/ I know that graphs.cospectral_graphs() gives all pairs of graphs with same eigenvalues. But I need graphs with same spectral radius i.e. largest eigenvalue (the other eigenvalues may be different) and differing in diameter and number of edges.
What to do for this? Thank you in advance.Deepak SarmaThu, 12 Apr 2018 00:47:21 -0500http://ask.sagemath.org/question/41990/Eigenvalues over symbolic ringhttp://ask.sagemath.org/question/45567/eigenvalues-over-symbolic-ring/I am trying to compute the eigenvalues of a 16x16 matrix whose eigenvalues are multivariate polynomials in 4 variables of degree at most 3 and integer coefficients. When I try to do so using the Symbolic Ring SR my machine quickly runs out of memory (~15GB available I believe).
TypeError: ECL says: Memory limit reached. Please jump to an outer pointer, quit program and enlarge the memory limits before executing the program again.
I am using sage 8.1 (and I could try to upgrade if that is the issue here). The example I am struggling with is included at the end of this question (I did not write this by hand, but I don't think that it is relevant how the matrix was generated. One should be able to copy-and-paste this into Sage)
I tried to change the ring to the fraction field of a Multivariate Polynomial Ring over Rational Field, and this allows to quickly compute the characteristic polynomial and its roots, without killing my machine. Unfortunately though some of the eigenvalues are not rational functions, so they do not show up. This is what I did
R = QQ['a,b,c,d']
N = matrix(R, 16, 16, M)
N.change_ring(R.fraction_field()).characteristic_polynomial().roots()
Mathematica on the same machine is able to compute the eigenvalues symbolically (quite quickly actually), and I can solve a similar problem in Sage if I only use 2 variables. Am I missing something, or is simply the algorithm used by Sage not efficient enough for 16x16 matrices in 4 variables?
----------
a,b,c,d = var('a','b','c','d', domain='positive')
M = matrix(16,16,[
(3*c^2*d + 6*c + 1, 0, 0, (a - b)*c*d + a - b, 0, (a - b)*c*d + a - b, (a - b)*c*d + a - b, 0, 0, (a - b)*c*d + a - b, (a - b)*c*d + a - b, 0, (a - b)*c*d + a - b, 0, 0, 3*(a - b)^2*d),
(0, -3*c^2*d + 1, (a + b)*c*d + a + b, 0, (a + b)*c*d + a + b, 0, 0, -(a - b)*c*d + a - b, (a + b)*c*d + a + b, 0, 0, -(a - b)*c*d + a - b, 0, -(a - b)*c*d + a - b, 3*(a + b)*(a - b)*d, 0),
(0, (a + b)*c*d + a + b, -3*c^2*d + 1, 0, (a + b)*c*d + a + b, 0, 0, -(a - b)*c*d + a - b, (a + b)*c*d + a + b, 0, 0, -(a - b)*c*d + a - b, 0, 3*(a + b)*(a - b)*d, -(a - b)*c*d + a - b, 0),
((a - b)*c*d + a - b, 0, 0, 3*c^2*d - 2*c + 1, 0, -(a + b)*c*d + a + b, -(a + b)*c*d + a + b, 0, 0, -(a + b)*c*d + a + b, -(a + b)*c*d + a + b, 0, (2*(a + b)^2 + (a - b)^2)*d, 0, 0, (a - b)*c*d + a - b),
(0, (a + b)*c*d + a + b, (a + b)*c*d + a + b, 0, -3*c^2*d + 1, 0, 0, -(a - b)*c*d + a - b, (a + b)*c*d + a + b, 0, 0, 3*(a + b)*(a - b)*d, 0, -(a - b)*c*d + a - b, -(a - b)*c*d + a - b, 0),
((a - b)*c*d + a - b, 0, 0, -(a + b)*c*d + a + b, 0, 3*c^2*d - 2*c + 1, -(a + b)*c*d + a + b, 0, 0, -(a + b)*c*d + a + b, (2*(a + b)^2 + (a - b)^2)*d, 0, -(a + b)*c*d + a + b, 0, 0, (a - b)*c*d + a - b),
((a - b)*c*d + a - b, 0, 0, -(a + b)*c*d + a + b, 0, -(a + b)*c*d + a + b, 3*c^2*d - 2*c + 1, 0, 0, (2*(a + b)^2 + (a - b)^2)*d, -(a + b)*c*d + a + b, 0, -(a + b)*c*d + a + b, 0, 0, (a - b)*c*d + a - b),
(0, -(a - b)*c*d + a - b, -(a - b)*c*d + a - b, 0, -(a - b)*c*d + a - b, 0, 0, -3*c^2*d + 1, 3*(a + b)*(a - b)*d, 0, 0, (a + b)*c*d + a + b, 0, (a + b)*c*d + a + b, (a + b)*c*d + a + b, 0),
(0, (a + b)*c*d + a + b, (a + b)*c*d + a + b, 0, (a + b)*c*d + a + b, 0, 0, 3*(a + b)*(a - b)*d, -3*c^2*d + 1, 0, 0, -(a - b)*c*d + a - b, 0, -(a - b)*c*d + a - b, -(a - b)*c*d + a - b, 0),
((a - b)*c*d + a - b, 0, 0, -(a + b)*c*d + a + b, 0, -(a + b)*c*d + a + b, (2*(a + b)^2 + (a - b)^2)*d, 0, 0, 3*c^2*d - 2*c + 1, -(a + b)*c*d + a + b, 0, -(a + b)*c*d + a + b, 0, 0, (a - b)*c*d + a - b),
((a - b)*c*d + a - b, 0, 0, -(a + b)*c*d + a + b, 0, (2*(a + b)^2 + (a - b)^2)*d, -(a + b)*c*d + a + b, 0, 0, -(a + b)*c*d + a + b, 3*c^2*d - 2*c + 1, 0, -(a + b)*c*d + a + b, 0, 0, (a - b)*c*d + a - b),
(0, -(a - b)*c*d + a - b, -(a - b)*c*d + a - b, 0, 3*(a + b)*(a - b)*d, 0, 0, (a + b)*c*d + a + b, -(a - b)*c*d + a - b, 0, 0, -3*c^2*d + 1, 0, (a + b)*c*d + a + b, (a + b)*c*d + a + b, 0),
((a - b)*c*d + a - b, 0, 0, (2*(a + b)^2 + (a - b)^2)*d, 0, -(a + b)*c*d + a + b, -(a + b)*c*d + a + b, 0, 0, -(a + b)*c*d + a + b, -(a + b)*c*d + a + b, 0, 3*c^2*d - 2*c + 1, 0, 0, (a - b)*c*d + a - b),
(0, -(a - b)*c*d + a - b, 3*(a + b)*(a - b)*d, 0, -(a - b)*c*d + a - b, 0, 0, (a + b)*c*d + a + b, -(a - b)*c*d + a - b, 0, 0, (a + b)*c*d + a + b, 0, -3*c^2*d + 1, (a + b)*c*d + a + b, 0),
(0, 3*(a + b)*(a - b)*d, -(a - b)*c*d + a - b, 0, -(a - b)*c*d + a - b, 0, 0, (a + b)*c*d + a + b, -(a - b)*c*d + a - b, 0, 0, (a + b)*c*d + a + b, 0, (a + b)*c*d + a + b, -3*c^2*d + 1, 0),
(3*(a - b)^2*d, 0, 0, (a - b)*c*d + a - b, 0, (a - b)*c*d + a - b, (a - b)*c*d + a - b, 0, 0, (a - b)*c*d + a - b, (a - b)*c*d + a - b, 0, (a - b)*c*d + a - b, 0, 0, 3*c^2*d + 6*c + 1)]
)angeloluciaWed, 27 Feb 2019 18:50:15 -0600http://ask.sagemath.org/question/45567/Fast numerical computation of eigenvalueshttp://ask.sagemath.org/question/44531/fast-numerical-computation-of-eigenvalues/I am trying to calculate the eigenvalues of a large (say, n=1000 to 10000) sparse Hermitian square matrix using SAGE
> numpy.linalg.eigvalsh(MyMatrix)
takes very long. I noticed it utilizes only a single core of my CPU.
How would one go about speeding the calculation? Specifically, I'm looking for a solution using parallel computation, or maybe something which is "more compiled".
Thank you.SageMathematicianSat, 01 Dec 2018 12:10:10 -0600http://ask.sagemath.org/question/44531/Eigenvalues of matrix with entries in polynomial ringhttp://ask.sagemath.org/question/8797/eigenvalues-of-matrix-with-entries-in-polynomial-ring/Hi!
I just wrote some code on the sage-combinat queue which computes a matrix with entries in a polynomial ring R = PolynomialRing(QQ, 'x', n)
sage: P = Poset(([1,2,3,4], [[1,3],[1,4],[2,3]]), linear_extension = True)
sage: L = P.linear_extensions()
sage: M = L.markov_chain_transition_matrix(labeling = 'source')
sage: M
[-x0 - x1 - x2 x3 x0 + x3 0 0]
[ x1 + x2 -x0 - x1 - x3 0 x1 0]
[ 0 x1 -x0 - x3 0 x1]
[ 0 x0 0 -x0 - x1 - x2 x0 + x3]
[ x0 0 0 x0 + x2 -x0 - x1 - x3]
sage: M.eigenvalues()
---------------------------------------------------------------------------
NotImplementedError Traceback (most recent call last)
/Applications/sage-5.0.beta7/devel/sage-combinat/sage/combinat/posets/<ipython console> in <module>()
/Applications/sage-5.0.beta7/local/lib/python2.7/site-packages/sage/matrix/matrix2.so in sage.matrix.matrix2.Matrix.eigenvalues (sage/matrix/matrix2.c:26415)()
/Applications/sage-5.0.beta7/local/lib/python2.7/site-packages/sage/matrix/matrix2.so in sage.matrix.matrix2.Matrix.fcp (sage/matrix/matrix2.c:11089)()
/Applications/sage-5.0.beta7/local/lib/python2.7/site-packages/sage/rings/polynomial/polynomial_element.so in sage.rings.polynomial.polynomial_element.Polynomial.factor (sage/rings/polynomial/polynomial_element.c:22655)()
NotImplementedError:
Is it possible to compute this some other way or is this just not yet implemented (which would surprise me!).
Thanks,
Anne
-----
Edit (originally posted as an answer by the original poster of the question)
Here is an easier example with the question:
sage: R = PolynomialRing(QQ, 'x', 2)
sage: x = R.gens()
sage: M = matrix([[x[0],x[1]],[x[1],x[0]]])
sage: M.eigenvalues()
---------------------------------------------------------------------------
NotImplementedError Traceback (most recent call last)
/Applications/sage-5.0.beta7/devel/sage-combinat/sage/combinat/posets/<ipython console> in <module>()
/Applications/sage-5.0.beta7/local/lib/python2.7/site-packages/sage/matrix /matrix2.so in sage.matrix.matrix2.Matrix.eigenvalues (sage/matrix/matrix2.c:26415)()
/Applications/sage-5.0.beta7/local/lib/python2.7/site-packages/sage/matrix/matrix2.so in sage.matrix.matrix2.Matrix.fcp (sage/matrix/matrix2.c:11089)()
/Applications/sage-5.0.beta7/local/lib/python2.7/site-packages/sage/rings/polynomial/polynomial_element.so in sage.rings.polynomial.polynomial_element.Polynomial.factor (sage/rings/polynomial/polynomial_element.c:22655)()
NotImplementedError:Anne SchillingFri, 16 Mar 2012 14:05:50 -0500http://ask.sagemath.org/question/8797/Eigenvalues of hecke operatorshttp://ask.sagemath.org/question/40588/eigenvalues-of-hecke-operators/For a project I am trying to build a program that computes a basis for cusp forms of weight 2 over $\Gamma_0(N)$. At one point, I want to represent eigenvalues of multiple Hecke operators. For example, (for $N=23$) I have found the following matrices for the Hecke operators:
$
T_2=\begin{pmatrix} -2 & -1/2 ;
2 & 1 \end{pmatrix}, T_3=\begin{pmatrix} 3 & 1 ;
-4 & -3 \end{pmatrix} \quad T_5=\begin{pmatrix} -2 & -1/2 ;
2 & 1 \end{pmatrix} \quad
$
so we have the following characteristic polynomials $f_2=x^2+x-1$, $f_3=x^2-5$, $f_5=x^2 +2x-4$. Suppose we denote the solution of $f_2$ (eigenvalues of $T_2$) by $a$ and it's conjugate. Then we can denote the solution of $f_3$ by $2a+1$ and of $f_5$ by $2a$.
I am trying to figure out how I can 'make' Sage represent these eigenvalues in this way. Say I have found these matrices above, I can create k.< a >=NumberField(x^2+x-1), then $a$ represents the root of the polynomial. So the question for me is, how can I make Sage give me the eigenvalues of $T_3$ and $T_5$ in terms of $a$?
Furthermore, I am wondering how to get the jordan normal form of $T_2$, or eigenmatrix in terms of $a$. If I ask for jordan_form, I get an error, and if I ask for eigenmatrix_right, I only get a numerical expression.
Remark: A little context, the goal for this project is to represent newforms in a similar way as Sage does, when you ask for example Newforms(23,2,names='a'). We need the eigenvalues of the hecke operators since they correspond with the coefficients of the Fourier series.
----------TheBeiramSat, 13 Jan 2018 04:32:29 -0600http://ask.sagemath.org/question/40588/command to get eigenvalueshttp://ask.sagemath.org/question/39621/command-to-get-eigenvalues/ If a matrix is given for heigher order ..i want to know how to get eigen values by sage.RajniThu, 16 Nov 2017 22:23:02 -0600http://ask.sagemath.org/question/39621/comparing sets of roots of charpolyhttp://ask.sagemath.org/question/35729/comparing-sets-of-roots-of-charpoly/ I am missing something about how to compare list of roots.
During a small algorithm I need to know wether a matrix has or not complex eigenvalues. I did the following
A=matrix(QQ,[[1,2,1],[6,-1,0],[-1,-2,-1]])
a=(B.charpoly()).roots(ring= QQ, multiplicities=False)
b=(B.charpoly()).roots(ring= QQbar, multiplicities=False)
then a is the list [-4,0,3] and b is the list [3,0,-4].
I don't get the following :
set(a)==set(b)
return false while
set([-4,0,3])==set([3,0,-4])
return true.
Any help, either on the first pb (knowing that a QQ matrix has complex eigenvalues) or on the second would be greatly appreciated.
Cheers.Laurent BThu, 24 Nov 2016 14:15:42 -0600http://ask.sagemath.org/question/35729/Eigenvalues/vectors of jacobian matrix as complex numbershttp://ask.sagemath.org/question/33049/eigenvaluesvectors-of-jacobian-matrix-as-complex-numbers/ Hello,
I'm trying to find the eigenvalues and eigenvectors of a jacobian matrix expressed as complex numbers (complex double field?), not an expression (like 1/2 * sqrt(...)...).
sorry for the silly question...
--------------------------------------------------------------------------
EDIT: Some more info; I'm studying a dynamical system at an equilibrium point. I would like to get an expression for the eigenvectors and values assosiated with the center eigenspace of a "hopf bifurcation".
Here is the code in question:
var('alpha1, alpha2, beta1, beta2, mu1, mu2, phi1, phi2, c1, c2, k1, k2, t ') ;
# suggested parameter values:
alpha1 = 0.7; alpha2 = 0.3
beta1 = 0.003; beta2 = 0.0015
mu1 = 0.6; mu2 = 0.4
phi1 = 2.3; phi2 = 4
c1 = 400000; c2 = 100
k1 = 0.0033100000000000;
k2 = 0.000988067680992286;
# The vector field and its jacobian matrix:
f(P, M, L, G,k2) = [phi1*M*(1-M/c1) - (alpha1 + beta1)* P - k1*P*G, alpha1*P - mu1*M, phi2*G*(1-G/c2) - (alpha2 + beta2)* L + k2*P*G, alpha2*L - mu2*G];
J = jacobian(f, (P, M, L, G));
# Equilibrium solution:
M4 =((alpha1*alpha2 + alpha1*beta2)*c1*c2*k1*mu1*mu2 + (alpha1^2*alpha2*c1*phi1 - (alpha1*alpha2*c1*c2*k1 + (alpha1^2*alpha2 + alpha1*alpha2*beta1)*c1)*mu1)*phi2)/(alpha2*c1*c2*k1*k2*mu1^2 + alpha1^2*alpha2*phi1*phi2);
P4 = ((alpha2 + beta2)*c1*c2*k1*mu1^2*mu2 + (alpha1*alpha2*c1*mu1*phi1 - (alpha2*c1*c2*k1 + (alpha1*alpha2 + alpha2*beta1)*c1)*mu1^2)*phi2)/(alpha2*c1*c2*k1*k2*mu1^2 + alpha1^2*alpha2*phi1*phi2);
L4 = -((alpha1*alpha2 + alpha2*beta1)*c1*c2*k2*mu1^2*mu2 - alpha1^2*alpha2*c2*mu2*phi1*phi2 - (alpha1*alpha2*c1*c2*k2*mu1*mu2 - (alpha1^2*alpha2 +alpha1^2*beta2)*c2*mu2^2)*phi1)/(alpha2^2*c1*c2*k1*k2*mu1^2 + alpha1^2*alpha2^2*phi1*phi2);
G4 = -((alpha1*alpha2 + alpha2*beta1)*c1*c2*k2*mu1^2 - alpha1^2*alpha2*c2*phi1*phi2 -(alpha1*alpha2*c1*c2*k2*mu1 - (alpha1^2*alpha2 + alpha1^2*beta2)*c2*mu2)*phi1)/(alpha2*c1*c2*k1*k2*mu1^2 + alpha1^2*alpha2*phi1*phi2);
# Now I evaluate it at the fixed point:
J4 = J(P=P4, G=G4, M=M4, L=L4)
J4 = J4(k2=k2)
Now if I do something like;
J4.eigenvalues()
I get an lengthy radical expression.
And when computing the eigenvectors:
D, P = J4.eigenmatrix_left()
I get an error...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "_sage_input_129.py", line 10, in <module>
exec compile(u'open("___code___.py","w").write("# -*- coding: utf-8 -*-\\n" + _support_.preparse_worksheet_cell(base64.b64decode("RCwgUCA9IEo0LmVpZ2VubWF0cml4X2xlZnQoKQ=="),globals())+"\\n"); execfile(os.path.abspath("___code___.py"))
File "", line 1, in <module>
File "/tmp/tmpYDeAbA/___code___.py", line 2, in <module>
exec compile(u'D, P = J4.eigenmatrix_left()
File "", line 1, in <module>
File "sage/matrix/matrix2.pyx", line 5617, in sage.matrix.matrix2.Matrix.eigenmatrix_left (build/cythonized/sage/matrix/matrix2.c:39965)
IndexError: list index out of rangeVillageIdiotSun, 10 Apr 2016 08:12:11 -0500http://ask.sagemath.org/question/33049/eigenvalues vs roots of characteristic polynomialhttp://ask.sagemath.org/question/31656/eigenvalues-vs-roots-of-characteristic-polynomial/Hi,
Sorry if this is a stupid question but I am struggling to make Sage compute the exact eigenvalues of a matrix.
I am also confused that when I ask for the roots of the characteristic polynomial Sage answers with complex roots...
I am new to Sage so please forgive me :)
Here is my worksheet:
sage: A = matrix([[1, 1, 2], [1, -2, 0], [2, 0, 1]])
sage: A
[ 1 1 2]
[ 1 -2 0]
[ 2 0 1]
sage: A.eigenvalues()
[-2.439311671683875?, -0.6611203141265045?, 3.100431985810380?]
sage: x = var('x')
sage: H = A.charpoly()
sage: H
x^3 - 8*x - 5
sage: H.roots()
[]
sage: (x^3-8*x-5).roots()
[(-1/2*(1/18*I*sqrt(1373)*sqrt(3) + 5/2)^(1/3)*(I*sqrt(3) + 1) + 1/3*(4*I*sqrt(3) - 4)/(1/18*I*sqrt(1373)*sqrt(3) + 5/2)^(1/3),
1),
(-1/2*(1/18*I*sqrt(1373)*sqrt(3) + 5/2)^(1/3)*(-I*sqrt(3) + 1) + 1/3*(-4*I*sqrt(3) - 4)/(1/18*I*sqrt(1373)*sqrt(3) + 5/2)^(1/3),
1),
((1/18*I*sqrt(1373)*sqrt(3) + 5/2)^(1/3) + 8/3/(1/18*I*sqrt(1373)*sqrt(3) + 5/2)^(1/3),
1)]
Laurent BThu, 17 Dec 2015 07:58:59 -0600http://ask.sagemath.org/question/31656/Problems in solving eigenvalue equations with differential operatorshttp://ask.sagemath.org/question/29398/problems-in-solving-eigenvalue-equations-with-differential-operators/Let's say we have a linear differential operator $\hat A = \sum_k a_k \frac {d^k} {dx^k}$ and we want to solve the eigenvalue equation $\hat A f(x) = a f(x)$ which is an ODE that we put in sage and outputs a solution $g(x)$. We now want to substitute $f(x)$ with $g(x)$ and simplify our expression in order to extract the eigenvalues of $\hat A$. The problem here is that I am not able to substitute the derivatives with my solution neither via `eqn.substitute_expression(f(x) == g(x))` nor via `eqn.substitute_function(f(x),g(x))` because `D[0]f(x)`, ... `D[0,0,...,0]f(x)` remain unchanged.
papachristoumariosThu, 03 Sep 2015 16:50:54 -0500http://ask.sagemath.org/question/29398/Condensing variables of a matrixhttp://ask.sagemath.org/question/27271/condensing-variables-of-a-matrix/I'm working with matrices such as
M = matrix([
[a, b, 0],
[c, 0, d],
[0, e, 0]])
where a, b, c, d, and e are variables. Then I loop through some numbers for each of a, b, c, d, and e, looking at the eigenvalues of the resulting matrix. $$ char(M) = x^3 - ax^2 - (bc + de)x + ade $$
So, I'm doing more work than necessary, and ideally, I'd reduce M down to
M = matrix([
[a, b, 0],
[1, 0, d],
[0, 1, 0]])
Is there a simple way of using Sage to do so?IcemanTue, 07 Jul 2015 12:16:55 -0500http://ask.sagemath.org/question/27271/Orthonormal basis consisting of eigenvectors of a matrixhttp://ask.sagemath.org/question/26525/orthonormal-basis-consisting-of-eigenvectors-of-a-matrix/ How to find an orthonormal basis consisting of eigenvectors of a matrix. We assume that the matrix is over reals.Uday BhaskarTue, 14 Apr 2015 04:21:01 -0500http://ask.sagemath.org/question/26525/eigenvalues of matrices in AAhttp://ask.sagemath.org/question/26357/eigenvalues-of-matrices-in-aa/ M=matrix(AA,[[0,-1],[1,0]])
M.eigenvectors_right()
raises an error "eigenvectors are not implemented for matrices with eigenvalues that are not in the fraction field of the base ring or in QQbar" which is just wrong because the eigenvalues of M are certainly in QQbar.
Can someone please explain how to avoid this problem?
Thanks,
Jaume
JaumeFri, 27 Mar 2015 04:41:04 -0500http://ask.sagemath.org/question/26357/Calculation of symbolic eigenvalueshttp://ask.sagemath.org/question/25240/calculation-of-symbolic-eigenvalues/ Hello,
I am very new to Sage. In my first trial, I sought for eigenvalues of a symbolic matrix. However, Sage returns the following error:
ArithmeticError: could not determine eigenvalues exactly using symbolic matrices; try using a different type of matrix via self.change_ring(), if possible
I have seen an example of eigenvalues of a symbolic matrix being calculated by Sage on another page. So I wonder what the problem is in this case. Below is my code:
var('s b')
A = matrix([[0,0,b,b,b,b,b,b,b,b],[s,0,0,0,0,0,0,0,0,0],[0,s,0,0,0,0,0,0,0,0],[0,0,s,0,0,0,0,0,0,0],[0,0,0,s,0,0,0,0,0,0],[0,0,0,0,s,0,0,0,0,0],[0,0,0,0,0,s,0,0,0,0],[0,0,0,0,0,0,s,0,0,0],[0,0,0,0,0,0,0,s,0,0],[0,0,0,0,0,0,0,0,s,0]]); A
A_evals = A.eigenvalues()
Many thanks for your support.kavir1698Fri, 12 Dec 2014 11:17:24 -0600http://ask.sagemath.org/question/25240/Solve the following system of ODE's and plot its solutionhttp://ask.sagemath.org/question/24852/solve-the-following-system-of-odes-and-plot-its-solution/Solve the following system of ordinary differential equations
d^2x/dt^2 + 5x + 2y = 0
d^2y/dt^2 + 2x + 8y = 0
with initial conditions x(0)=1, y(0)=2, x'(0)=-4, y'(0)=2
and plot its solution as a curve in the {x,y} plane.fomel_sergeyWed, 12 Nov 2014 19:21:22 -0600http://ask.sagemath.org/question/24852/Black box numerical optimization of a convex functionhttp://ask.sagemath.org/question/23831/black-box-numerical-optimization-of-a-convex-function/I would like to numerically optimize a convex function without using any of its internals, that is, a python function. Is there an implementation of this in sage? I tried `sage.numerical.optimize.find_local_minimum` but it fails internally with a
TypeError: unable to find a common ring for all elements
My function to optimize is in fact the second largest eigenvalue of a matrix that is constructed from one parameter. Here it is in all gory detail:
def binaryStrings(k):
for i in range(2**k):
s = str(bin(i))[2:]
yield "0"^(k-len(s)) + s;
def hammingDistanceInt (a,b):
return bin(a^^b).count("1")
def cubeAdjacency (k):
# Note: We would like to use QQ instead of CDF, but this will
# result in inexact computations failing due to rounding later
# (Yes it does!)
# https://groups.google.com/forum/#!topic/sage-support/3IIbu0OBJX4
return matrix(CDF, 2^k, 2^k, lambda i, j: 1 if hammingDistanceInt(i,j)==1 else 0);
def hemmeckeFiberAdjacency (k, p1):
p2 = (1 - 4*k*p1)/2;
M = p1 * block_diagonal_matrix (cubeAdjacency(k),cubeAdjacency(k));
M[0,2^k] = p2
M[2^k,0] = p2
rowsums = M * vector ([1]*2^(k+1))
M += diagonal_matrix(vector([1]*2^(k+1))-rowsums);
return M
def slem(k,p):
e = map(abs, hemmeckeFiberAdjacency(k,p).eigenvalues())
e.sort();
return e[-2];
def slem4(p): return slem(4,p)
plot(slem4, [0,1/16]) # Works fine
sage.numerical.optimize.find_local_minimum(slem4, [0,1/16]) # Type errorThomasTue, 19 Aug 2014 05:43:57 -0500http://ask.sagemath.org/question/23831/QZ decomposition for generalized eigenvalueshttp://ask.sagemath.org/question/10751/qz-decomposition-for-generalized-eigenvalues/[QZ decomposition @Wiki](http://en.wikipedia.org/wiki/Schur_decomposition#Generalized_Schur_decomposition)
[QZ factorization @MATLAB](http://www.mathworks.de/de/help/matlab/ref/qz.html)
Can we use SAGE to solve a generalized eigenvalue problem?
Thanks in advance!gundamlhWed, 20 Nov 2013 22:26:24 -0600http://ask.sagemath.org/question/10751/Why does jordan_form not work over inexact rings?http://ask.sagemath.org/question/10488/why-does-jordan_form-not-work-over-inexact-rings/Hi,
Given a matrix M with entries (variables) in SR, I needed to compute the transformation matrix to a jordan form of M.
I ended up copying the code in "jordan_form" and "_jordan_form_vector_in_difference" from "matrix2.pyx",
deleting the "if (base_ring is None and not self.base_ring().is_exact()) ..."
and replacing "evals = A.charpoly().roots()" by
eigenvects=A.eigenvectors_right()
evals=[(eigenvect[0],eigenvect[2]) for eigenvect in eigenvects]
So far it seems to work. Can this go wrong? Or could one just change the original code in matrix2.pyx, and allow inexact rings?
Thanks for your help!LolinaWed, 28 Aug 2013 23:43:36 -0500http://ask.sagemath.org/question/10488/Plotting eigenvalues as a function of a variablehttp://ask.sagemath.org/question/9675/plotting-eigenvalues-as-a-function-of-a-variable/I am attempting to plot the the eigenvalues for the matrix:
H=matrix([[1+x, 0, x],[0, 2, 2*x],[x, 2*x, 1+x]])
which were calculated using the following method:
a=H.eigenvalues()
in the following way:
h=fast_callable(real_part(a[2]),vars=[x],domain=CC)
plot(h,(0,0.5))
but unfortunately this does not work for a[0] and a[1],
f=fast_callable(real_part(a[0]),vars=[x],domain=CC)
g=fast_callable(real_part(a[1]),vars=[x],domain=CC)
plot(f,(0,0.5))+plot(g,(0,0.5))
Any suggestions would be greatly appreciated.
wrighteapTue, 01 Jan 2013 08:30:29 -0600http://ask.sagemath.org/question/9675/Sorted list of symbolic eigenvalues (and corresponding eigenvectors)http://ask.sagemath.org/question/9599/sorted-list-of-symbolic-eigenvalues-and-corresponding-eigenvectors/Is there a way to obtain a sorted list of eigenvalues when they are computed symbolically (in SR). Particularly knowing that in specific points, they can switch order.
So far, what I have is (assuming $R^3$):
def sorted_eval(m, x, y, z, order=0):
_ev = m.eigenvalues()
_ev = numpy.array(ev.subs(x=x, y=y, z=z))
_ev.sort()
return _ev[order]
But then if I want to perform a contour plot:
x, y, z = var('x y z')
p = vector([x,y,z])
f = p * p
h = f.hessian()
contour(lambda x, y: sorted_eval(h, x, y, 0, 0), (x, -1.5, 1.5), (y, -1.5, 1.5))
It takes a long time
Thanks
D
DemMon, 03 Dec 2012 07:08:01 -0600http://ask.sagemath.org/question/9599/eigenvalues of a derivative vs derivative of eigenvalueshttp://ask.sagemath.org/question/9543/eigenvalues-of-a-derivative-vs-derivative-of-eigenvalues/Hi! I have this little problem. If anyone would be so kind to share his knowledge and shed some lite on it, I'd be very grateful. Big thanks in advance (and sorry for my english)!
I have a matrix M=M(x) depending on a variable x. I want sage to compute trace of a product of a derivative of M, M' and some function of it, f(M), at a fixed value of x=x_0; that is:
(tr[M'*f(M)])|_(x=x_0).
It just so happens that tr[M'*f(M)] = sum( ev_i' *f(ev_i) ), where {ev_i(x)} are eigenvalues of M. Lucky me. Diagonalisation of M commutes with differentiating or taking the function of it, one could say.
But my M and its derivative are somewhat complicated, yet simplify greatly after substituting x=x_0. So I would very much prefer first to compute M', substitute x_0 M0:=M|_(x=x_0) and M'0:=M'|_(x=x_0), and only after that ask sage for eigenvalues:
ev1=M0.eigenvalues()
ev2=M'0.eigenvalues()
So here's the question: do i have any reason for hoping that:
(tr[M'*f(M)])|_(x=x_0) = sum( ev2[i] *f(ev1[i]) for i in range(dim of M) )?
(That is, wether the order of eigenvalues changes if I exchange diagonalisation with differentiation?)ozikSat, 17 Nov 2012 12:18:33 -0600http://ask.sagemath.org/question/9543/