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3h
comment How to determine why Solve[] failed?
Possibly the issue is that Solve is now using different methods (due to a restriction that a variable be real-valued), and these methods might be slower in this case than those for handling general complex-valued solutions. As Solve does not use the latter first, it has no way to realize that the solution set is empty. This is just speculation on my part in that I've not checked, but it is a likely explanation.
5h
comment How to determine why Solve[] failed?
Solve[x == 1 && y == 2, {x}] returning an empty solution set is correct, and documented behavior, and not related to the rest of the post as best I can tell. As for the documentation, see the Details section in the ref guide page for Solve: "With MaxExtraConditions->Automatic, only solutions that require the minimal number of equational conditions on continuous parameters are included." In this case, there is an equational condition imposed, to wit, y==2, and the default setting is MaxExtraConditions->0.
8h
comment Why does Mathematica say $\int_0^1\int_0^1\int_0^1\frac{1.0}{xyz}\,dz\,dy\,dx=0$?
I should add that my remarks do not mean I am happy with the present situation regarding multivariate definite integrals. Just that there is no quick resolution in terms of Integrate internals.
8h
comment Finding the numerical solution to a polynomial of a high degree
Since you have a couple of constrained parameters, why don't you use FindMinimum or NMaximize on the cost function?
8h
comment please help me with this question
Wrong site. Not that I favor posting homework to any site.
9h
comment A bug in Integrate
@Dr.Wolfgang Hintze I have no objection if MSE adds a category such as IntegrateAnomalies. I think it is safe to say, though, that exact definite integrals involving parametrized path singularities are going to be a thorny area.
9h
comment Missing zero in the CoefficientList
One thing to be aware of is that CoefficientList can take a third argument indicating a total length, and will pad out with zeros to meet that length. This can be used to enforce that the lists being multiplied have the same length.
1d
comment How to speed or help Solve[] when it is stuck?
@Guess who it is I don't actually know how much trouble it is, or even what exactly Eliminate is now doing. It might be that it was never overhauled in the way that Solve was. Or maybe it was, and is falling short for other reasons.
1d
answered How to speed or help Solve[] when it is stuck?
1d
comment How to speed or help Solve[] when it is stuck?
(1) Solve is fine with Solve[list==0] and just quietly thread over one level. (2) I suspect Eliminate is not happy with inequalities though.
1d
comment Why does Mathematica say $\int_0^1\int_0^1\int_0^1\frac{1.0}{xyz}\,dz\,dy\,dx=0$?
Were that default behavior in Mathematica to change, many multivariate integrals it currently handles would simply hang.
1d
comment Why does Mathematica say $\int_0^1\int_0^1\int_0^1\frac{1.0}{xyz}\,dz\,dy\,dx=0$?
By the way, comments will go automatically only to original posters and whoever gave the particular response under which the comment appears. I only saw the answer request by accident. To reach anyone else e.g. another commenter, be sure to use the "at" sign to get their attention (it's kind of like raising from the spirit world, I think).
1d
answered Why does Mathematica say $\int_0^1\int_0^1\int_0^1\frac{1.0}{xyz}\,dz\,dy\,dx=0$?
1d
comment Equation solution using minimization
Same question also appears on Wolfram Community here (You really should mention and link when a question is cross-posted). The function is difficult to evaluate in certain ranges, which is almost certainly why FindRoot apparently has problems with it.
1d
comment Finding the numerical solution to a polynomial of a high degree
I cannot tell what it is that is being asked.
1d
comment CharacteristicPolynomial returns 0
The presence of machine numbers is infectious. So if there is a possibility for catastrophic cancellation, say, then that could indeed be the cause of an unexpected result of 0.0.
1d
comment Does the equation have two roots?
In what way is it difficult to check the results?
1d
comment How to speed up a symbolic integration
There are a number of parameters and telling it that the entire expression is real (which is done incorrectly above, should use Reals where you have Real) is not sufficient to unravel possible branch cut crossings. This is an issue for the subexpression Log[1 + mgl^2/sa1 - x].
1d
comment system of nonlinear partial differential-algebraic equation
Did you happen to notice some constants with no numerical values provided/ Pic and kr0? Or that sqrt is in there where you almost certainly want Sqrt (the language is case sensitive)? You really need to check things more carefully before asking the entire readership to find the problems in your code.
1d
revised system of nonlinear partial differential-algebraic equation
added semicolon so it will cut/paste/parse