# MaplePrimes Questions

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### solving pde with a piecewise condition numerically...

June 05 2011
1 4

Hello all,

I am trying to solve a pde system with piecewise conditions numerically but unsucessful. Here's what i am doing:

> restart;

> sys:=[diff(c(x,t),t)=v(x,t)*diff(c(x,t),x$2),diff(v(x,t),t)=piecewise(c(x,t)>v(x,t),c(x,t)*diff(v(x,t),x$2),0)];

> bc:={c(0,t)=2,c(1,t)=1,c(x,0)=0,v(0,t)=1,v(1,t)=2,v(x,0)=0};

> sol:=pdsolve(sys,bc,type=numeric,time=t);

I am getting the following error.......

Error, (in pdsolve/numeric/process_PDEs...

### Transient Heat Transfer Problem...

June 05 2011
0 7

Hello,

I am trying to solve a transient heat transfer problem.

The problem is that I have an insulated pipe that is immersed in cold water.  At time 0, the fluid filling the pipe is at a constant temperature.  The insulation at one end of the pipe is different to the rest of the insulation.  I need to find out the time that it would take any fluid to reach a certain temperature, called the cool down time.

A graphic representation of the...

### asymptotic limit...

June 05 2011
1 1

Is there an easy way to find the limit of the following equations as Pec_i approches infinity.

Equation 1

(Q*(R*S+1-S)/(1-R*R3*k*(1-R1)/C/Pec_i*S)*(H_vap+1/(1-exp(Pec_i)))*exp(C*Pec_i/(R*S+1-S)*(1-R*R3*k*(1-R1)/C/Pec_i*S)*S/k)-H_vap)*(1-exp(Pec_i*(1-S)/(R*S+1-S)*(1-R*R3*k*(1-R1)/C/Pec_i*S))) = 1;

Equation 2

Theta0/C = (exp(Pec_i/(R*S+1-S)*(1-R*R3*k*(1-R1)/C/Pec_i*S)*(1-S))-1)*(H_liq+1/(1-exp(-C/k*Pec_i/(R*S+1-S)*(1-R*R3*k*(1-R1)/C/Pec_i*S)*S)));

### why pdsolve have found functions with same name bu...

June 05 2011
1 6

when try to solve this pde, got error

i know function h already, just try to guess its pde, initial value condition is calculated from known function

motion := {diff(h(x1,x2), x1)^2 + 2*diff(h(x1,x2), x1)*diff(h(x1,x2), x2) + diff(h(x1,x2), x2)^2 = 0};
ic := {h(1,x2)=ln(1-x2-(1/2)*c),h(x1,0)=ln(1-(1/2)*c*x1)/x1};
monster := pdsolve(motion union ic);

Error, (in pdsolve/sys/info) found functions with same name but depending on different arguments in the given DE system: {h(1, x2...

### How can i write this structure function?...

June 04 2011
1 2

1-(1-x1)(1-x2)....(1-xn)=1-(inverted PI).

Is there a simbol for the Inverted PI?

thanks

### Does this series converge?...

June 04 2011
1 8

Does the series sum((-1)^floor(ln(n)^2)/n, n = 1 .. infinity) converge?

### Understanding the simplify function - different op...

June 04 2011
2 3

Please help me to make sense of the ways to use the simplify function. In this particular case Maple does some computation and gives me some huge output which I paste below. When I try to simplify the huge output Maple just hangs. But if I use varied commands of simplify detailed below such as simplify(huge_output,symbolic)  or  simplify(huge_output,size)  Maple gives me an output but none of the output are equal to each other and I also noticed that in one instance...

### without multiseries and selecting poles with posit...

June 04 2011
1 1

Okay so I can see how to get the poles. But I have some further questions.

1) For beta AND Q both GREATER THAN 0 WHICH poles have positive imaginary part and is there a PROGRAMMATIC way of selecting these ones?

2) How do I calculate the residue at these poles? The approach given by Alec above seems useful and is much...

### Matlab-Maple interface...

June 03 2011
0 7

Dear fellow users,

I am trying to call Maple functions from Matlam .m file. How can I do it?

I am using Matlab 7.12 (R2011a) and Maple 12.

### How to use fsolve to get all roots in a range...

June 03 2011
0 1

Dear Maple users,

I am trying to solve a non linear equation for complex and real roots and I am using following command:

answer:=fsolve(func,x,{x=-100-100*I..100+100*I},complex); % here 'func' is a nonlinear function

to search for all possible roots in the given range. But fsolve does not return all possible roots. Mostly it returns one. But I am sure the function has more roots in the specified range

But, if my "func" is simple polynomial (e.g. func= x^5-3x^2+3x-1...

### Writing Procedures inside of For Loops...

June 03 2011
1 10

I'm trying to write a for loop that will generate several procedures, which doesn't quite seem to work as expected.

Here is the sample code:

for j from 1 to 2 do
f[j]:=proc(x,y)
x+y^(j)
end proc;
od;

Then if you run the following, you get:

f[1](x,y) = x+y^3

f[2](x,y) = x+y^3

Whereas, I'd like to have:

f[1](x,y) = x + y^1

f[2](x,y) = x + y^2

Any suggestions on why the j value...

### Solving poisson equation...

June 03 2011
0 4

Hi there,

I am new to Maple. I need to solve a non-homogeneous partial differential equation (eg. poisson equation:

pd := expand(Laplacian(u(r,phi))=g(phi))

where g(phi)=Acos(phi)

My problem is that when I try to use the command  pdsolve, I get wrong answer. Cant maple solve a non-homogeneous equation directly? Do I need to guide it to solve the problem? How?

I am stuck with this problem for many days. :(

### Using assume or assuming to eliminate added terms...

June 03 2011
0 1

I would like to be able to enter an assumption into maple indicating one variable is much greater than another.  I would then like maple to eliminate the smaller variable term when it is added together with the much greater term.  However when I use the >>> symbol in maple along with assuming I get an error.

> eqn1 := y = a*t+b*t;
...

### Repeated complex differentiation...

June 03 2011
1 1

Hi,

I want to apply a complex differential operator to an expression "polynomial in the imaginary part * differential operator".

I have been unable to figure out how to do that using a formal operator and a concrete one that takes care of differentiating the polynomial.

In more detail:

Let $d$ be (my complex number is $x+iy$)

$d:=\frac{\partial}\partial x}- i\frac{\partial}{\partial y}$

which I want to apply to

$p(y) d$

### dsolve event handling question, general...

June 02 2011
1 3

dsolve event handling looks like a great tool, but I can't understand how it works and it's not sufficiently popular to google my way to examples online. There are two things I'd like to do: 1) interrupt the computation once some variable leaves a certain range, 2) interrupt the computation if the solver gets stuck into an infinite loop. Both are documented in the help, but I don't understand it. Suggestions welcome, thanks!

http://www.maplesoft.com/support/help/Maple/view...

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