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20170603 00:29:02 +0200  answered a question  How to decide if T maps R^5 onto R^5 Just compute the rank of the matrix: 
20170602 19:12:44 +0200  asked a question  a problem with variables in real domains Hi, I have a problem with setting the domains of definition of variables. For example, typing I get the result Where I'm wrong? thanks! 
20170602 11:24:34 +0200  asked a question  Efficient algorithms for simplification Hi!
I come back on an issue on Sage/Maxima, about simplification.
I have some large rational polynomial expressions in say ten variables that I would like to simplify.

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20160920 08:49:21 +0200  commented answer  how to kill a variable @paulmasson: thanks, corrected! 
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20160919 10:31:20 +0200  answered a question  how to kill a variable 
20160908 19:36:29 +0200  asked a question  Automorphisms and derivations of Lie algebras Is there a way to compute automorphisms and/or derivations of a Lie algebra (of dimension 4)? Thanks in advance! 
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20160121 18:42:05 +0200  commented question  Dimension of a certain subspace of a matrix space I can not edit, still. Here below a translation: Write a function in Sage, with the aim to compute the dimension of the vector subspace $W \subseteq \mathrm{End}(M_n(\mathbb{R}))$ constructed as following: W consists of linear maps $F(A;B) \colon M_n(\mathbb{R}) \to M_n(\mathbb{R})$ such that $F(A;B) \colon X \mapsto AX + XB$ with $A$, $B$ in $M_n(\mathbb{R})$. Here, $n\geq 2$. 
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20160111 12:29:49 +0200  asked a question  rank of matrices depending on parameters Hi! I have a question on how to treat objects depending with parameters. For example, let M be a matrix depending on a parameter  call it t. The rank command just returns the generic rank. I would like to know the rank of the matrix, varying the parameter. In the example, I would like to get: if t=0, the rank is 1; otherwise is 2. Is there any command for this in Sage? (I've heard about a "full solve" in Mathematica.) Thanks in advance, 
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20160104 17:48:08 +0200  commented question  assume a variable has two possible values dear Thierry, what kind of assumptions are not taken into account? and what do you mean by "not taken into account"? the problem is related to a reseach problem I'm studying. I should try to write a sample example. Roughly speaking, I have objects in a Lie algebra (whose structure equations may depend on parameters), and I am declaring objects with variable coefficients. Some additional properties add constraints on the possible values of the coefficients. I am using assume() to take into account the several properties. Thanks in advance, all the best, 
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20160103 14:49:04 +0200  asked a question  Extract equalities from a list of assumptions Hi, how can I recognize an equality from an inequality, in a list of assumptions? thanks, 
20160102 23:53:00 +0200  asked a question  assume a variable has two possible values Hi, how can I assume that a variable admits only a finite number of possible values? E.g., the variable x can only be 0 or 1. I could assume that
but I am looking whether there is a straightforward way, too. thanks in advance 
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20151204 11:34:49 +0200  asked a question  order of assume I am working on cloudsagemath. I have a question on how "assume" works. I type: when I check the output the first time with shift+enter, I just get
The second time, I get the expected answer:
Why? how to force the second answer since the beginning? thanks in advance! 
20151204 10:05:49 +0200  asked a question  Substitution of parameters I would like to understand what is the correct and more efficient way for performing sostitution of parameters in objects of some category. For example, a typical problem for me is the following. I have a 1form in an ExteriorAlgebra, whose coefficients depends on some variable, let's say t. I find conditions on such parameters, let's say, t should be zero in order that some property holds. (In general, i will have solutions of linear systems.) I try to use "substitute" for setting the parameter to be 0, but this does not work to me.. Another solution I tried is the following. I assume t==0 at a certain point. But this seems to me to force the substitution before too. Thanks in advance for any suggestions! 
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20150114 12:11:18 +0200  answered a question  dictionary substitution for elements of ExteriorAlgebra at the end, i solved by myself: the dictionary has to be compatible with the exterior structure  clearly.. so, it works with: 