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I'm the little trashcan that could!


17h
comment Solving simultaneous systems of linear equations
In other words, use LinearSolve[Join[A1,...,An], Join[b1,...,bn]].
17h
comment Fitting to a power law — is there any reason to fit a line to the log of the data instead?
Just to sum up what everyone else said, for noise-free (perfect) data the two fit results will be the same. However, for real data with noise, the fits will be slightly different.
21h
comment Simplify returns wrong result
As Bob Hanlon points out, using /. is a quick and easy way to perform substitutions, but it may not always give correct answers in cases where singularities are involved, and to rigorously evaluate a function limit at a particular point, you should instead use Limit[..., x -> x0].
21h
comment How to differentiate a function?
Assuming your data is good, computing the difference sequence should suffice. If you have noisy data and V10, you can apply a Savitzky-Golay differentiator using SavitzkyGolayMatrix.
21h
comment Simplify returns wrong result
This is a duplicate of a question asked last week, give me a minute and I'll post a link.
23h
comment Replace Exp by Sinh and Cosh
Use DSolve[eqn, v[x], x] // ExpToTrig.
1d
awarded  Nice Question
2d
comment Maxwell propagator problem 2D
I thought this exact question was asked a couple days ago, but now I can't find it. In any case, have you tried looking for a minimal working example?
2d
comment Bug? Or what? Why it returns internal functions?
Can't reproduce on V10.0.1 Mac OS X 10.6. It almost sounds like you've got a virus eating your system files LOL.
2d
revised Mathematica Lattice Reduce Command
added 252 characters in body
2d
answered Mathematica Lattice Reduce Command
Nov
18
revised Minimization problem in a subset of Complex matrices
added 68 characters in body
Nov
18
answered Minimization problem in a subset of Complex matrices
Nov
17
awarded  Nice Answer
Nov
16
comment I have the best fit, How can wiggle a plane between the max and min errors
What does "move the plane of best fit through the maximum and minimum error" mean? If you just want the signed projected distances of the points from the best fit plane, you can just use the third right singular vector from the SVD method I proposed in my previous answer to your plane-fitting direction. Also, your code is not minimal working, since t is not defined.
Nov
15
comment Array in Sum in Minimize - error “Part specification x[1] is neither a machine-sized integer”
@dio: I think what the OP is trying to do is minimize the given sum, where the x[i] are integers between 1 and 10. Part is getting unhappy at the fact that the x[i] are being treated as variables, and I don't know how to fix this, so I'd be interested to see what the correct syntax for this is.
Nov
15
comment If works wrongly under Table or Sum
Why do you think that is wrong? Since j is not defined, each if-statement has indeterminate value, and thus correctly returns the table where the j are all symbolic.
Nov
15
comment How to calculate improper integral
Use Solve[Integrate[ Exp[(-(1/450))*(x - 50)^2]/(15*Sqrt[2*Pi]), {x, r, Infinity}] == (2*141.21)/90000, r], which yields r -> 90.995. A few points: first, you need to use Boolean equals ==, rather than Set =, and second, in the future you should include actual code, rather than a picture of a screen with code.
Nov
15
comment Polynomial with alternating sign coefficients from the odd degree terms of a Truncated Power Series
@BobHanlon: Yup, you're right, it looks like it fails when $f$ doesn't have a convergent series (and I imagine there's cases where it fails even when it does), edited answer to address this. It does seem to work with $f(x)=\log(1+x)$ though, presumably because it has a convergent series.
Nov
15
revised Polynomial with alternating sign coefficients from the odd degree terms of a Truncated Power Series
added 60 characters in body