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Feel free to correct the grammar mistakes in my posts.


8h
comment Integrate does not accept my integrand expression
The integration with Assumptions option inside Integrate just finished and it gave back the input 囧. A friend of mine has also tried Maple 18 but it gave back the input (Maybe it's because he isn't good at Maple? ). Also, when m = 0, the result isn't actually f Pi/m but f Pi (1 - 2 Log[R]). As to the integration without assumptions, the results of that from 0 to 2 Pi and from -Pi to Pi seem to be the same when Element[m, Integers], and though a direct substitution of m won't work, we can get a simplified result for a specific m with Limit.
10h
comment Integrate does not accept my integrand expression
You're right. Seems to be a bug at least to v8.0.4. BTW, if I introduce the assumptions with Assumption option of Integrate, the calculation seems to last forever. Maybe you can report it to Wolfram company?
11h
comment Integrate does not accept my integrand expression
v8.0.4 evaluates to 0.
1d
comment If doesn't compile if its output is the output of Compile?
@OleksandrR. In fact it's that question that motivate me to ask this one (I've noticed this behavior for some time), I read it but still failed to notice it's an identical issue 囧.
1d
comment Linear interpolation over 2 variables
It's hard to give suggestions without a specific code sample, can you add one?
2d
comment Derive a PDE from other PDEs
In addition, to avoid downvotes I suggest you to show your specific effort on solving this rather than just pasted the question here and vaguely said you have "read some material". BTW, you forgot to give the definition of $\rho$.
2d
comment Compile with array operations
@brama Er……for example, you've used a lot of AppendTo, I'm not sure if it's because you're following the rule of thumb "the more my code inside Compile looks like C code I'd write otherwise, the more I benefit from it", but if it's what your original code looks like, you'd better set some effort on avoiding it. BTW, AppendTo is even disliked inside Compile, see this post for details. A complete discussion for this issue might need a whole book 囧, have you already read Leonid's excellent book?
2d
comment Compile with array operations
@brama See my edit. (Links for CopyTensor are added above Update.)
Apr
16
comment Solving System of Nonlinear with Three Differential Equations
@bobthechemist OK, let me elaborate it into an answer.
Apr
16
comment Dsolve is not solving equation ( 3 system with 2.order diferantial equations)
I think you're looking for @b.gatessucks right? :D
Apr
16
comment Dsolve is not solving equation ( 3 system with 2.order diferantial equations)
Well, so v9 can solve this set of equations? With v8.0.4, I only got the original input returned…
Apr
16
comment Solving System of Nonlinear with Three Differential Equations
Then you must have once mixed up = and ==. You need Clear[Derivative]. Values stored in Derivative can't be cleared by Clear["Global`*"] because it actually means clearing all the variables under context "Global`" while Context[Derivative] gives "System`".
Apr
16
comment Derive a PDE from other PDEs
You can refer to this post: mathematica.stackexchange.com/a/6428/1871
Apr
15
comment Compile with array operations
Precisely speaking, I suggest you to at least avoid function definition based on pattern-matching. (see this post for details. )
Apr
15
comment ParallelTable, ParallelDo and ParallelMap all fail on simple evaluations, a BUG?
possible duplicate of Definitions inside ParallelTable?
Apr
15
comment ParallelTable, ParallelDo and ParallelMap all fail on simple evaluations, a BUG?
I think you need SetSharedVariable[Data].
Apr
15
comment Compile with array operations
Several observations: 1. qsum = MapThread[Plus, #] &@Rq can be changed to qsum=Total@Rq, 2. qsum = N[Plus @@ Fq] can be embedded into the definition of qf, 3. kr = ReplacePart[#, (\[Alpha] delta/Vf), 1] & /@ kr can be changed to kr[[All, 1]] = \[Alpha] delta/Vf. There still exists warnings but I'd like to stop here, as I mentioned above, I don't think compiling these code makes much sense.
Apr
15
comment Compile with array operations
Can you make some effort on reproducing your problem in a minimal code sample? BTW, I doubt even if you fix your code, it'll be slow since it has made so many external calls in Compile.
Apr
14
comment Plotting Fourier spectrum versus frequency of a signal
Your suggestion for changing sample size to 2048 and using a triangle does work (if I've understood it correct). Maybe you can consider improving your answer when you become more familiar with Mathematica, most people here are not familiar with signal processing after all :D
Apr
12
comment Solution To Nonlinear System
Or have I misunderstand your equations? Does those notations mean $\begin{array}{ll} \{ & \begin{array}{ll} (\text{r1}-\text{x1})^2+(\text{r2}-\text{x2})^2+(\text{r3}-\text{x3})^2==f \\ \text{r1} \text{z1}+\text{r2} \text{z2}+\text{r3} \text{z3}==\text{y1} \text{z1}+\text{y2} \text{z2}+\text{y3} \text{z3} \\ \frac{\text{r1} \text{v1}+\text{r2} \text{v2}+\text{r3} \text{v3}-\text{v1} \text{x1}-\text{v2} \text{x2}-\text{v3} \text{x3}}{\sqrt{(\text{r1}-\text{x1})^2+(\text{r2}-\text{x2})^2+(\text{r3}- \text{x3})^2}}==d \\ \end{array} \\ \end{array}$