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2017-08-24 01:34:04 -0500 answered a question collect variables buried in an expression

It sometimes helps to expand and factor:

sage: s
1/4*(2*D*Nb*Pmean - (D*H*alpha + D*H)*c)/((alpha + 1)*c)
sage: s.expand()
-1/4*D*H*alpha/(alpha + 1) - 1/4*D*H/(alpha + 1) + 1/2*D*Nb*Pmean/((alpha + 1)*c)
sage: _.factor()
-1/4*(H*alpha*c - 2*Nb*Pmean + H*c)*D/((alpha + 1)*c)
sage: _.partial_fraction()
1/4*(2*Nb*Pmean - (H*alpha + H)*c)*D/((alpha + 1)*c)
2017-08-24 01:21:27 -0500 commented answer Sage not returning roots of polynomimal

sage: print([SQ[i*2][0].minpoly().degree() for i in range(16)]) [32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32]

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2016-11-08 10:43:16 -0500 commented question What is the problem with that integral ?

Simplification: sin(atan(y)) = y/sqrt(1+y^2) could be applied.

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2016-11-04 09:43:20 -0500 answered a question Use cumulative distribution functions

Using the actual function I get a fine plot via:

sage: CDFlogn(x,nu,sigma) = 1/2*(1+erf((log(x)-nu)/(sigma*sqrt(2))))
sage: plot(CDFlogn(x,1.5,.6),0,10)
Launched png viewer for Graphics object consisting of 1 graphics primitive

sage: CDFlogn(x,1.5,.6)
1/2*erf(-0.833333333333333*sqrt(2)*(-log(x) + 1.50000000000000)) + 1/2
sage: CDFlogn(4,1.5,.6)
1/2*erf(-0.833333333333333*sqrt(2)*(-log(4) + 1.50000000000000)) + 1/2
sage: CDFlogn(4,1.5,.6).n()
0.424846794957399

For example: https://en.wikipedia.org/wiki/Log-nor...

2016-11-04 09:23:56 -0500 commented answer Use cumulative distribution functions

Then at the moment you need to create your function in mathematical terms. Please see and rate my answer.

2016-04-03 00:19:24 -0500 commented question Memory saturation when I test equalities in symbolic ring.

Or before. I also cannot confirm with 7.2.beta2

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2015-10-24 09:24:08 -0500 commented answer qepcad failing to replicate examples

qepcad did install here on 6.10.p1 after I set my MAKE to make -j1.

2015-10-19 01:38:53 -0500 answered a question does SAGE compute Pi using Chudnovsky algorithm?

Sage uses the mpfr library to compute pi to arbitrary precision. The mpfr algorithm apparently has a limit of 646456992 digits. Please refer to

https://github.com/epowers/mpfr/blob/...

Not sure if that is up-to-date, however.

2015-10-15 01:35:31 -0500 answered a question sage doesn't evaluate

Use simplify_full:

sage: f(x) = sum(k,k,0,x)
sage: f
x |--> 1/2*x^2 + 1/2*x
sage: f(x) = sum(binomial(10,k),k, 0,x)
sage: f
x |--> sum(binomial(10, k), k, 0, x)
sage: f(2)
sum(binomial(10, k), k, 0, 2)
sage: f(2).simplify_full()
56
2015-10-14 08:52:53 -0500 commented answer Plot doesn't seem to evaluate my function

That's a bug that already has a fix which just needs to be reviewed: http://trac.sagemath.org/ticket/9424

2015-10-04 08:00:02 -0500 answered a question simplify_rational gives different results

Your proj is ab.dot_product(n)/n.norm()^2*n so your tt*n.norm() is ab.dot_product(n)/n.norm()^2 * n.norm() which is different from proj.norm() because the norm() in tt*n.norm() only applies to n. You made the same mistake when you equaled (tt*n.norm()).simplify_rational() and tt*n.norm().simplify_rational(). Here in the latter the simplify_rational() only applies to n.norm().

Operator precedence in Sage closely follows the same in Python (but in C++ for example the dot would have behaved the same way).

2015-10-04 03:26:53 -0500 commented question Multivariate Laurent series

This is right.Multivariate Laurent series are not implemented in Sage at the moment.

2015-09-27 09:39:58 -0500 commented answer simplify sqrt(x/y^2)*y

A fix should be possible with pynac-0.4.x (pynac is part of Sage); pynac git master already does sqrt(x^2) --> x for x>0 as side effect of other changes.

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2015-09-25 02:16:08 -0500 commented answer Understanding the 'solve()' result with braces and brackets ("([{x:z},{x:y}],[1,1])")

The y:z can be deduced from the other two, but I have no idea how the results come up specifically.

2015-09-21 02:50:22 -0500 commented answer simplify sqrt(x/y^2)*y

Miguel, note that sqrt(x^2) != x for x<0.

2015-09-15 08:20:27 -0500 commented question High memory usage when substituting variables

Maybe http://trac.sagemath.org/ticket/17494 is related. In any case the output of get_memory_usage() increases too.

2015-09-15 08:05:15 -0500 commented question High memory usage when substituting variables

I confirm the steady increase. This is not reduced by gc.collect(). Maybe it is a Singular issue (Singular is used by Sage in case of multivariate polynomials).

2015-09-15 07:41:34 -0500 answered a question Understanding the 'solve()' result with braces and brackets ("([{x:z},{x:y}],[1,1])")

The result consists of two lists: [{x: z}, {x: y}] and [1, 1]. Each list is a possible result that solves the equation. The first list is a Python dictionary (which by definition has no order but gives the values that specific variables will need to satisfy the equation); the second is a list (which simply gives the needed values for the variables in the order the vars were given as argument. Substitution confirms:

sage: P.subs(x==z)
0 == 0
sage: P.subs(x==y)
0 == 0
sage: P.subs(x==1,y==1)
0 == 0
2015-09-09 01:17:18 -0500 answered a question Forcing Symbolic Variables to Always be Real

First, with the newest versions of Sage the domain you create a variable with is propagated to the assumption database so you can say:

var('R r L omega k s', domain='real')

I am not sure how you get to the output you give, I got:

sage: Z(s,L) = s * L
sage: Z.diff(s)
(s, L) |--> L
sage: Z
(s, L) |--> L*s
sage: Z(R,r,L,k,omega,s) = R + I * omega * L + ((s * omega**2 * L**2 * k**2) * (r - I * omega * L)) / (r**2 + omega**2 * s **2 * L**2)
sage: Z.diff(s)
(R, r, L, k, omega, s) |--> -2*(-I*L*omega + r)*L^4*k^2*omega^4*s^2/(L^2*omega^2*s^2 + r^2)^2 + (-I*L*omega + r)*L^2*k^2*omega^2/(L^2*omega^2*s^2 + r^2)
sage: Z
(R, r, L, k, omega, s) |--> (-I*L*omega + r)*L^2*k^2*omega^2*s/(L^2*omega^2*s^2 + r^2) + I*L*omega + R

Also, you say that the derivative should be zero. But that's only the case if s is a constant, no?

2015-08-27 02:01:40 -0500 answered a question Inverses of matrices of Laurent polynomials

This is defined behaviour of the general inverse, as far as I understand from the code. For example,

 sage: parent(~1)
 Rational Field

The definition of Matrix_generic_dense.__invert__() explicitly states

Return this inverse of this matrix, as a matrix over the fraction field.

sage: R.fraction_field()
Fraction Field of Univariate Polynomial Ring in t over Integer Ring

I'm not an algebraist so no comment on that but, with symbolics you would stay in the ring, so symbolics seems to be good for something, contrary to many a belief.

sage: mat = matrix([[x^2]])
sage: mati = mat.inverse(); mati
[x^(-2)]
sage: mati[0,0].parent()
Symbolic Ring
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2015-08-21 01:28:29 -0500 commented question (Unexpanded) symbolic inequalities yield erroneous results

This was fixed in one of the 6.8 betas so 6.8 or 6.9 should be fine.

2015-08-08 04:06:06 -0500 commented answer Simplify result of this definite integral

That's not an anwer fitting in this forum.