# MaplePrimes Questions

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### Default method used in pdsolve/numeric...

Yesterday at 3:51 PM
2 0

I read in the net that the method used in pdsolve numeric is the theta method, my question: is it the most efficient with regard to rate of convergence of the numerical solution of the PDE?

If not then why is it used as the default method?

Thanks.

### How to find eigenvectors in terms of mmm?...

Yesterday at 3:06 PM
0 2

nullspace or reducedform or Eigenvectors still can not find eigenvector in terms of  mmm , how to find this?

mmm is a variable

### What is the difference ...

Yesterday at 3:05 PM
0 3

in eigenvector using nullspace and eigenvector using maple function  Eigenvectors ?

### How to find a soft line break in a string?...

Yesterday at 2:17 PM
0 4

I'm reading a string from a textbox, and I need to know where the line breaks are. Hint:They are not found by searching for \n.

### Reduction of Order for PDE (Substitution)...

Yesterday at 1:23 PM
1 0

I am trying to reduce a nonlinear PDE with the indendent variables $(x,y,t)$ and the dependent variable $\psi(x,y,t)$. $a,b,c$ and $r$ are constants.

I want to use the following substitution:
zeta=(-ax+by)/b, gamma=(bt-x)/b, lambda(zeta,gamma)=exp(-c*exp(rt))u(x,y,t)

This is what I have tried so far:

My first approach using convert function:

restart:
with(PDETools):
declare(psi(x,y,t),lambda(zeta,gamma));
tr:={(-ax+by)/b=zeta,(bt-x)/b=gamma};
eq1:=psi->PDE-equation;
eq2:=eq1(e^{ce^{rt}}*lambda((-ax+by)/b,(bt-x)/b);
eq3:=convert(algsubs(tr,eq2),diff);

This gives me an error: "Error, invalid input: algsubs expects its 1st argument, p, to be of type algebraic = algebaric, but received{(t*u[infintity]-x)/u[infinity]=gamma,....}"

Another approach using dchange:

restart:
with(PDETools):
declare(psi(x,y,t),lambda(zeta,gamma));
eq1:=0=PDE-equation;
tr1:={zeta=(-ax+by)/b,gamma=(bt-x)/b,lambda(zeta,gamma)=-e^{ce^{rt}}*psi(x,y,t)};
tr2:=sove(tr1,{x,y,t,psi(x,y,t)});
eq2:=dchange(tr2,eq1,[zeta,gamma,lambda(zeta,gamma)]);

Here I get the error: "Error, (in dchange/info) found {t} in both lhs and rhs of ´1st. set´ of transformation equations.

### Question about Export As LaTeX...

Yesterday at 10:12 AM
0 4

Dear All,

I am using the comand " export as" form the file menu to obatain a latex version of my worksheet. The generated latex file use a package called amplestd2e.sty that should be loaded for latex compiler to function proper. Do somebody know where to find it. Thank you. N. Jand

### How can I find explicit relations between columns ...

April 27 2016
2 7

Hi everybody!

I am trying to find explicitely the relations between the columns of a matrix

of non-maximal rank. For example, if I have the matrix

M := Matrix([<1,2,3>, <2,4,6>, <5,6,7>]);

I would like that Maple finds that the second column is twice the first one: v_2 = 2*v_1.

How can I do?

### Reverse the order of a list...

April 27 2016
0 2

How to reverse the order in a list?

example:

i have m := [1, 1, 0, 0, 1, 1, 1, 0]

I want to get the output like newm:=[0,1,1,1,0,0,1,1].

How to solve? Any command can help?

### Error when solving ODE system...

April 27 2016
0 3

hi.please see attached file below and help me.thanksode.mw

### How to add comma to binary number?...

April 27 2016
1 3

if m:= [01100101, 01101100, 01100111, 01100001];

I want to get [[0,1,1,0,0,1,0,1].[0,1,1,0,1,1,0,0],[0,1,1,0,0,1,1,1],[0,1,1,0,0,0,0,1]];

Any command can solve? Thank you.

### Problem with differential operator...

April 27 2016
0 7

hi.please see attached file below and help me.one problem is apply differential operator on matrix and then caclute 3D integral?

maple2.mw

 (1)

 (2)

 (3)

 (4)

 (5)

 (6)

 (7)

 (8)

 (9)

### Intersection of real intervals...

April 27 2016
2 3

Let A and B two real closed intervals.
I define b(x) as B+x for any real x ; more precisely, if B=[B1, B2], b(x) = [B1+x, B2+x]

I want to build a function f(x) such that :

1. if  A and b(x) do not overlap then f(x) = 0
2. otherwise f(x) is some expression of the covering length

For example : if A=[0, 2] and B=[-2,-1], then

1. f(x) = 0 if  -1+x < 0 or -2+x > 2
2. otherwise f(x) = L   where L is the measure of the intersection of A and b(x)

I coded a few variants using piecewise or Heaviside functions.
In some sense I have already answered my own question ... but no one is neither elegant nor concise.

I wonder if there exist a Maple function that returns the measure of the intersection of two real intervals (when they overlap) and 0 otherwise ?

### Problem with symbolical solution...

April 27 2016
1 1

Hi,

I have been trying to solve the following equation with respect to y, but I have not been successful. In fact, I always get answer RootOf(...). I should mention that all variables and parameters are real non-negative. I have also tested with "assume", but it did not help. Any suggestion would be appreciated.

 (1)

 (2)

 (3)

Thanks.

### Data in Worksheet...

April 26 2016
0 1

How much MB of data one can compile in single worksheet without fear of crashing?

I asked this question because I have maple worksheet with almost 1000 of lines, initially sheet use to open very quickly but as soon as data started piling up the opening of worksheet slowdown significantly.

Should I worry about such slowdown due to large amount of data in worksheet or should I need to create another worksheet to divide data??

Regards

### Problem with coefficients in PDEtools...

April 26 2016
1 4

hi,

i want to compute the determining PDE system satisfied by the infinitesimals, such as the KdV equation.

but i have a problem, if i use the command

DeterminingPDE(PDE1, integrabilityconditions = false, split = false)

i can get the coefficients of independent objects, but u[t] exists.

i want to replace u[t] by (-u[x]u-u[x,x,x]), then extract the coefficients.

but i can't collect the coefficients.

my code:

with(PDEtools, DeterminingPDE, declare, diff_table, casesplit, InfinitesimalGenerator, Infinitesimals, SymmetryTest, ReducedForm, FromJet, ToJet);

declare(u(x, t));

U := diff_table(u(x, t));

PDE1 := U[]*U[x]+U[t]+U[x, x, x] = 0;

DetSys := DeterminingPDE(PDE1, integrabilityconditions = false, split = false);
detsys := FromJet(DetSys, u(x, t), differentiationnotation = diff);
pd1 := subs(U[t] = -U[]*U[x]-U[x, x, x], detsys); #u[t]->(-u[x]u-u[x,x,x])
pd2 := ToJet(pd1, [u(x, t)]);

how do i collect the coefficients?

help!

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