Mac Dude

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12 years, 215 days

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These are replies submitted by Mac Dude

Your problem starts at the line x:=0. This causes Maple to read x(t) to be 0(t) to be 0. You cannot use x as function and as a value at the same time.

if x:=0 is really meant to be the initial value x(0)=0, then ignore that for now; solve the general case and then insert the initial values.

If you wan to to it numerically, the IVs go into the dsolve(...,numeric) command. RTFM.

M.D.

 

The function is called Heaviside (capital H). Also, your Heaviside(0)-Heaviside(1) makes no sense; I guess what you want is Heaviside(x)*Heaviside(1-x); which is an impulse 1 unit long.

With these changes dsolve returns a solution but it cannot evaluate it. I don't know what is wrong, and I don't have time to trouble-shoot it, my apologies.

Mac Dude.

 

Is it even clear there is a solution? Faced with a situation like yours I suggest you spend the time understanding what your system is about. It appears you are mixing linear and multilinear terms, with some complex constants thrown in. You can, e.g., try to solve subsets of increasing complexity and see what you get. You can try to solve for some variables if they appear to show up in only a few eqns. and thereby reduce the number of variables in the final solution attempt. Even better if you can break down the whole problem into self-contained pieces you can solve individually.

Just throwing a large system at any CAS is (in my experience) not usually a promising strategy even if, at times, one gets lucky. Of course, you can always run the thing overnight or a weekend... again, I have not had much luck with that approach.

Mac Dude.

 

 

@ Well, I think it is time to make that phone call. I don't want to play with my own installation to verify it, but I think soap.dat is needed for a single-user installation (which is what I have and presumably you as well). I assume customer service can verify that you have a "legal" license and maybe let you reinstall or help you in other ways.

M.D.

 

@Arilson Mar Can you describe a specific problem to tackle?

M.D.

@ I checked my own installation. The licensing files appear to reside in

/Library/Frameworks/Maple.framework/Versions/15/license/

(and you notice that here I have a relatively old version). In this directory I have two relevant files (plus two text files):license.dat and soap.dat. License .dat is installed by the installer whereas soapfile appears not to (judging by the installer log). You may want to check whether you have both of these. License.dat sems to be mostly a list of packages etc. that are included. Soapfile is an xml file that amongst others has the "purchase code" (the code you have to type in upon activation) as well as another number that may encode the host you activated on. Both of these are readable with a regular editor (Emacs, TextWrangler or similar).

If license.dat is not there I assume you'll need to get it back from your backup. You did backup before the system upgrade, right? In fact, you could even try to restore the whole license directory.

If that does not work; then maybe something more is bollixed. You could try to reinstall Maple (assuming that your license allows for more activations).

Good luck,

Mac Dude.

@trigo1 The addition of two (or more) sinusoidal functions with different frequencies creates terms with sum and difference frequencies (often called beat frequencies). So if you have omega1 and omega2 you'll get in general 4 frequencies (the originals and the beats), each one having its own amplitude (related to A and B).

Maple's facilities to ferret that out are not strong or intuitive. Playing around a little with your formula it seems that working with the exponential representation (convert(expr,exp)) allows for more strength in manipulations using Maple's facilities. If you want to stay with sines and cosines you may have to roll your own sum and difference rules although I seem to recall there are some packages that help this along.

If A=B, the original frequencies vanish and you are left with the two beats (trivially shown by sum and difference rules for sine functions).

This link has a number of Maple worksheets possibly useful in this context:

http://www.peterstone.name/Maplepgs/trigfcns.html

So, it can probably be done, but you are unlikely to end up with a simple, pleasing answer.

Mac Dude

 

@birdiestreaming Just to be clear: you HAVE to adhere to the rules of Maple if you want reliable results. You said that just fixing the spelling of Pi gave you a result. But how do you know it is the correct result??? There are a good number of cases where Maple will give you a result, but not the one applicable because the problem was posed in the wrong way.

Caveat Computor! There is little or no room for sloppyness here, esp. when you are just starting out with Maple.

Mac Dude

I would use the Physics:-Vectors package to tackle this. See the docs on the physics package and its various subpackages (here esp. the Vectors subpackage). Once you spell "Nabla" correctly (with a "b" before the "l") it'll know what it means and knows how to do grad, div and curl.

Mac Dude

 

I don't think there is a built-in checkpointing procedure in Maple (checkpointing = writing state of a calculation to disk so you can resume from that point later). Assuming you have a kind of loop, you can save intermediate results; this thread may be helpful:

http://www.mapleprimes.com/questions/202512-How-To-Save-The-Session-Of-Maple-Worksheet#answer209792

You could e.g. wrap the save-state code into a proc & call that periodically.

If it is the intermediate state of one operation you want to save; I don't know how to do that.

M.D.

@rit With a shared kernel, ALL variables defined at the Maple prompt ARE global to both sheets (I just checked, as I do ot usually run in that mode).

Mac Dude

@Carl Love You are absolutely correct. Sockets are still outside of my Maple experience, but from a cursory look into the help it seems like that is what the OP may want to investigate.

Citation from the helpfiles:

The Sockets package is a suite of tools for network communication in Maple. The commands in this package enable you to connect to processes on remote hosts on a network (such as an Intranet or the Internet) and exchange data with these processes. In particular, it enables two independent Maple processes running on different machines on a network to communicate with one another.

Mac Dude

@Alejandro Jakubi This part of the op is (highly) suggestive that it is periodic:

"the value of the integrand at zero = the value of the integrand at 2*Pi."

In fact, I'd call that a sine function :-) maybe with an offset...

Seriously, though, it could be a number of things. We need more info.

M.D.

@georgepan Can you post the data file also? Copy-paste from your previous version (the Maple sheet with the data included) does not copy-paste correctly for me (no line endings) so I cannot use the data.

M.D.

@amrramadaneg Ok, I really do not see the joke part in my reply to your question. Please do not take it personal, but a post with misspellings, asking a question with no details given and therefore basically unanswerable => I do not expect a mature being behind this.

Seriously though, if you wrote the trapezoid routine yourself, then you'll have to either debug it yourself or post it here together with a test case exhibiting the problem.

If you used Student[Calculus1][ApproximateInt] (which per the docs is a trapezoidal-rule integrator), then be aware that Maple has a number of industrial-strength numeric integrators that you ought to be at least aware of and see whether they give you a better result. Look for int/numeric in the help facility. There are a number of integrators with different strengths and weaknesses, and for stiff or non-stiff problems. For each, there are a number of parameters that affect the outcome (like stepsize, convergence criterion etc.), and you probably have to explore different settings for these if your problem is ill-conditioned.

If you want help here I suggest strongly you create a test case displaying the problem and upload it. Yes, it may be a pain, but how do you expect people to help you otherwise? And, btw, you may want to do this for yourself to understand what is going on and how to fix it.

... this coming from someone who actually has used Maple's numeric integrators repeatedly for real-world problems, and at times struggled with them. While there are problems just too ill-conditioned to be solved in this way without being reformulated; I have found Maple's integrators on the whole to be quite powerful.

M.D.

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