MaplePrimes - Maple 16 Posts and Questions

logarithmic derivative?

abenigma — Sun, 19 May 2013 11:49:53 Z

how can i preform this calculation in maple?

(&PartialD;)/(&PartialD; log(R[e[0]]))(log(N[u]))

it's a derivative of a logarithmic expression with respect to another logarithmic expression, the one on the bottom is a "standalone" vairable and the one on the top is a function of the previous one and some others.

thaks in advance to anybody who might help.

How to export data from a PDE using using Export (Matrix)?

J4James — Wed, 15 May 2013 01:30:35 Z

Hello every one,

Here I will recall the PDE and its numerical solutiion provided by Maple help.

PDE := diff(u(x,t),t)=-diff(u(x,t),x);

IBC := {u(x,0)=sin(2*Pi*x),u(0,t)=-sin(2*Pi*t)};

pds := pdsolve(PDE,IBC,numeric,time=t,range=0..1);

p1:=pds:-plot(t=0,numpoints=50):
p2:=pds:-plot(t=1/8,numpoints=50,color=blue):
p3:=pds:-plot(t=1/4,numpoints=50,color=green):
plots[display]({p1,p2,p3});

I want to export data...

Differentia Equations Mixing Problem

BeeMariex3 — Fri, 10 May 2013 21:02:48 Z

Hi, I have a maple project and one of the questions reads:

a. | Initially, a 100 liter tank contains a salt solution with concentration 0.5 kg/liter. A fresher solution with concentration 0.1 kg/liter flows into the tank at the rate of 4 liter/min. The contents of the tank are kept well stirred, and the mixture flows out at the same rate it flows in.
i. Find the amount of salt in the tank as a function of time.

ii. Determine the concentration of salt in the tank at any time.

Simplification of bessel equations

maplelearner — Sun, 05 May 2013 12:21:15 Z

Dear Experts,

I have an equation which needs to be simplified. However it is mostly in Bessel I and BesselK. To simply it I have used the simplify( expression,

Can't compute mean or variance of custom discrete random variable

Gaussler — Sat, 04 May 2013 22:01:50 Z

Hi,

I'm trying to compute the mean and variance of a custom discrete random variable, as indicated in the file below (well, I do know its mean and variance, but I need the variable in a more complex context). Defining it is no problem at all, but when I parse Mean(Y) and Variance(Y), a weird expression shows up, despite my random variable being really simple. Does somebody know what goes wrong?

3d phaseportrait

kst11 — Tue, 30 Apr 2013 14:28:05 Z

Hi,

I'm trying to make a phase plane plot for the Lorenz system of differential equations around the equilibrium point (0,0,0) but when it keeps coming up with an error, saying it's "unable to obtain field plot, additional unknown(s) found: xy"

Any idea where I'm going wrong? Any help would be greatly appreciated!

Katie

solve ordinary differential equations

_zgj — Tue, 30 Apr 2013 12:51:05 Z

sys1 := [diff(y(x), x) = a/(1-y(x))^b+c*exp(-d*x)/(1-y(x))^2]:

dsolve(sys1)

but the result is empty.

What can I do?

random sample testing

askstatshelp — Sat, 27 Apr 2013 18:22:58 Z

I am trying to get Maple to calculate this for me:

Let X₁,X₂,...X₈₁ be a random sample from a distsribution (not necessarily normal) with mean µ=49 and standard deviation σ =8. Let ¯X = (1/81)* ∑_i=1⁸¹* X_i

_{I need to find the mean, the standard deviation and the approximate distribition of ‾X,}

_{BTW, the 81 goes directly...}

Problems solving IVP from MapleSIM in Maple / problems with fsolve

teh_allchemist — Fri, 26 Apr 2013 16:52:44 Z

Hi,

I've been trying to manipulate the equations of a mechanism that I've exported from MapleSIM. The system equations contain 4 differential ordinary equations, and 6 algebraic equations. In MapleSIM it simulates fine, but I'm having problems simulating it in maple alone (without multibody exports).

I've tried solving the initial value problem by replacing all the time dependant variables with constants, (and as this is a dynamics problem) I supplied...

Incorrect computation result

eddyliu — Thu, 25 Apr 2013 07:26:14 Z

The operation: 2^29.403243784 gives me 7.0999999820*10^8.

However, using WolframAlpha, the answer is 7.10000000139658667836958142950829925944726171959 × 10^8.

These are 2 different answers. Can someone offer an explanation as to why this occurs and how I can avoid this problem?

Thanks in Advance!

Eddy Liu

Error, (in HTTP:-Get) timed out waiting for initial response from server

marc005 — Tue, 23 Apr 2013 09:33:47 Z

I have this csv file on my website (the file is hosted on dropbox.com) that I want to load into Maple:
Hence I type:

URL := "https://dl.dropboxusercontent.com/s/7fqalrdtn0c3r8u/Stockholm%20Stock%20Exchange%28Percentage%20Change%29.csv?token_hash=AAGxpzva90O6oNlLAie3T1h0UNP06I5EPg2qrROHMglRMw&dl=1":
HTTP:-Get(URL, 'timeout' = 100)

Then I get:

Error, (in HTTP:-Get) timed out waiting for initial response from server

If you past the url into...

a question about iteration

HDN46 — Tue, 23 Apr 2013 07:30:20 Z

Here is a relation: t[n+1]:=((a*n^2+a*n+b)*t[n]+c*(n^2)*t[n-1])/(n+1)^2

t[-1]:=0 and t[0]:=1

a,b,c are integers and a,b,c are from 1 to 20 and n is from 0 to 20

the series t[n+1] is integer

I want to know how to list (a,b,c) that satisfies the above. Please help!

pdetest vs. algsubs

Karla — Mon, 22 Apr 2013 10:22:26 Z

Why is there a difference between pdetest and algsubs for a PDE?
Shouldn't pdetest work the same as algsubs for the example below?

restart: with(PDEtools):

Eq:=u(x,t)*diff(u(x,t),t)=0:

tmp:=sin(w*(c*t-x))-(1/4)*epsilon*c^2*cos(w*(c*t+x))^2+epsilon*c^3*w*cos(w*(c*t-x))*sin(w*(c*t-x))*t+(1/4)*epsilon*c^2*cos(w*(c*t-x))^2+(1/8)*c^4*epsilon^2*sin(w*c*t+w*x)+(1/8)*c^4*epsilon^2*sin(w*c*t+w*x)+(1/24)*c^4*epsilon^2*sin(3*w*c*t+3*w*x):

sol:=u(x,t)=tmp:

Can Maple evaluate this limit

DJJerome1976 — Sun, 21 Apr 2013 02:55:49 Z

I am attempting to apply some routine tests to determine the convergence of series with positive terms. I have run into a little difficulty with the root test. I am using surd( ) as shown below, but Maple will not give the exact value, which in my example, should be exp(6). Why is this happening and is there a way to get the root test to work?

Thanks!

Problem with Map

syn_burz — Sat, 20 Apr 2013 01:13:37 Z

I tried to use the parallelized Map function in Maple 16.

The following code worked as expected:

with(Threads);
Map(`^`,[1,2],2);

But then I tried:
Map(`op`,[[a,b]]);

and the Maple kernel crashed. This happens every time.

Any ideas what can be a reason of this?