929 reputation
1719
bio website wolfram.com
location United States
age 37
visits member for 3 years, 9 months
seen 2 days ago

The gravatar was made with Mathematica, and inspired by this.

The contents of my posts are my own opinion, and do not reflect the opinions of my employer.


Nov
23
comment Compute $\mathbf v \mathbf A^{-1}\mathbf v^\top$ in a numerically stable way
I found cholesky in the parallel directory: decompositions.
Nov
23
answered Compute $\mathbf v \mathbf A^{-1}\mathbf v^\top$ in a numerically stable way
Nov
21
revised Finding the derivative of two integrals and establish their equality.
reworded title
Nov
21
suggested suggested edit on Finding the derivative of two integrals and establish their equality.
Nov
17
comment Possible bug in Mathematica?
Also, Integrate doesn't do anything with an integer assumption (see the comments), so you have to watch out for them yourself.
Nov
17
comment Possible bug in Mathematica?
Sorry, mixing messages there. $\int^\pi_{-\pi} \cos(qx) = 2$ when $q = 0$, but $0$ otherwise. But, you get the wrong answer if you integrate first and then set $q=0$. So, I was wondering if we're running into something similar with regards to $r$ in your integrals, but I didn't write it out as fully as I should have.
Nov
17
comment Possible bug in Mathematica?
I have no idea why it ends being the exact negative. A guess is that like $\int^\pi_{-\pi} \cos(qx)$ with $q\in\mathbb{Z}$, there are multiple solutions depending on $r$, and by not fixing its value, Mathematica blithely chooses the incorrect one.
Nov
17
answered Taking advantage of linearity of integration in Mathematica
Nov
17
comment Possible bug in Mathematica?
Some quick notes. Symbolically integrating both pieces, I get (-i r^2 + r^(3/2) (i FresnelC[Sqrt[r]] + FresnelS[Sqrt[2]]))/Pi for $\int f$ and its negative for the second integral. However, integrating them both with a definite value of $r$, I get different results. For $r=5$, the sum is $1.19-5.00i$, and for $r=6$, the sum is $3.30-9.00i$, rounded, of course. I wonder if this is similar to the problem of integrating $\cos(q x)$ with $q \in \mathbb{Z}$.
Nov
16
comment How to solve integral in Mathematica?
Can you do me a favor and give some details as to the mathematics problem you're trying to solve? If we can understand what it is you're trying to accomplish, we may be able to provide better answers.
Nov
16
comment How to make Runge-Kutta for solving nonlinear ODE system in Mathematica
@George, I just downloaded your notebook, and in it you're using the form \[DifferentialD]f/\[DifferentialD]t which is incorrect as DifferentialD has no meaning by itself. Instead, you're looking for \[PartialD].
Nov
15
comment How to make Runge-Kutta for solving nonlinear ODE system in Mathematica
@Georde, also the NDSolve plug-ins tutorial gives explicit detail of setting up an RK4 integration. Admittedly, not all of it is germane to your question, but it does lay out the algorithm for you.
Nov
15
comment Group under matrix multiplication
As an added point, since your inverse did not have the same form as the other elements of the group, you should have been immediately suspicious of it, especially since you have already proven closure.
Nov
15
revised Group under matrix multiplication
added align to bring eqns inside bounding box.
Nov
15
suggested suggested edit on Group under matrix multiplication
Nov
12
awarded  Fanatic
Nov
9
comment What an Hermitian power of a normal matrix say about the original matrix?
@dan, your argument is circular. $(QDQ^{-1})^{*} = QDQ^{-1}$ relies on $A$ being Hermitian. If $A$ is normal, then it may have complex eigenvalues, so $D^{*} \neq D$.
Nov
9
comment Calculate periodicity in 1-dimensional array with noise
Here's a tutorial on correlations in Mathematica. It's late here, so I don't have time to write up a complete answer.
Nov
8
comment How to solve integral in Mathematica?
@George, my apologies for not getting back to you sooner. I have a couple of questions. Why should $H$ be diagonal? I don't see any reason, a priori, why it should be. So, I'd check to see that c[n,m], h, and g are giving you what you expect. If not, let me know what you expect them to be, and we'll see if we can get them there.
Nov
4
comment How to solve integral in Mathematica?
@George, give me several hours to get back to this. I'll take a look at it then.