December 10 2007
dvir 76
i need to solve a set of linear equations of size 7000x7000 using 128 digits, the system is sparsed. which of the "options" in LinearAlgebra[LinearSolve) is the the most efficient? is there more efficient builtin procedure for such computations?
thank's

Hi I have constructed a do loop to represent an epidemic described by 3 equations. I have plotted these using the initial conditions given.
If i want to identify the values of S[k], I[k] and R[k] at k=60 how do i enter this?
And how do i find out the exact point where the epidemic reaches its peak?

> p:=x->log[b](x);
p := x -> log[b](x)
> o:=x->b^x;
x
o := x -> b
> fsolve( p(x) = o(x) , {x,b} );
Error, (in fsolve) number of equations, 1, does not match number of variables, 2
I need to find the location (x,y) where they touch each other, thanks for the help.

In trying to answer the second question in

How to determine the order of an ODE? I have unsuccessfully tried to use

`select`

to filter out the appropiate parts of the differential equations.
In these attempts I have hit upon a behaviour of

`select`

I do not understand: In my opinion each of the following two code lines (or at the very least the second line) should return the differential expression itself:

select(has,diff(y(t),t),y);
select(has,diff(y(t),t),y(t));

But they do not; each line returns

`diff(y(t))`

, where the variable

`t`

with respect to which is being differentiated is missing. Why? Is it just me having fundamentally misunderstood something?

Although this question might seem silly to Maple experts, I cannot help asking, since despite a long search through Maple Help and Maple Guides I was not able to come across the answer. What I mean is this:
```
> eq1 := diff(y(t),t)-y(t)^2+y(t)*sin(t)-cos(t) = 0;
> # here I want some command that would return the order of eq1, i.e. 1
> something(eq1);
```

```
> eq2 := diff(y(t),`$`(t,2)) = y(t)*u(t) + diff(u(t),t);
> something(eq2,y); # this should return 2
> something(eq2,u); # this should return 1
```

Besides, I would also need the same for recurrent (shift) equations, i.e.

November 28 2007
hakon 28
Hi,
I'm trying to solve a set of simultaneous equations, and the solutions I get are expressions of _Z. I'd be most grateful if anyone could explain what this means.

How would i go around solving these equations?
1.) **5(7y+3)=39**
2.) **20(21r+40)=100**

(I think this was posted in the wrong section of mapleprimes.)
Hi,
I have read the manual on saving to a file many times but it never works for me.
I am using Maple 10 on a Mac running MacOS 10.4.10.
I have copied the example from the manual and run that and it does work so I am quite confused.
Here is what I would like to do: I have a worksheet with lots of definitions,equations, lists, etc. and I would like to have these available on another worksheet. I have tried
> save nx; # nx is the name of my worksheet
then
> read nx;
Error, unable to read `nx`
I have the same problem with trying to save names e.g.

Hello.
I'm having a problem graphing the following parametric equations in 3d , together:
x=1-2*t
y=-t
z=3+t
and
x= 5+3*s-4*t
y=7-5*s-5*t
z=-2-s+6*t
Thanks, excuse-me my English, I’m foreigner

November 15 2007
pippo 24
hello to everyone! I have a problem with the maple toolbox for matlab: i can't use the command setmaple to move my equations from matlab to maple. An example: i create two symbolic variables in matlab
>>syms x y;
then i set:
>>cos(x+y)
ans =
cos(x+y)
and now i try to move the equation to maple:
>>setmaple ('h',ans)
??? Undefined function or method 'setmaple' for input arguments of type 'sym'.
i'm using maple 11.01 and matlab 7.4.0. I tried updating toolbox for matlab but it didn't work. Some suggestions? Thanks...

Show that an n x n unitary matrix has n^2 - 1 independent parameters. {Hint: Each element may be complex, doubling the number of possible parameters. Some of the constraint equations are likewise complex and count as two coordinates.}
Next Question:
The special linear group SL(2) consists of all 2 x 2 matrices (with complex elements) having a determinant of +1. Show that such matrices form a group.
{Note: The SL(2) group can be related to the full Lorentz group in Section 4.4, much as the SU(2) group is related to SO(3).
Taken from "Mathematical Methods For Physicists", Arfken and Weber.

hi
i know a little bit about maple, i am able to input commands for it to solve non-power series equations
but i do not know how to input commands for solving equations involving the Sine Integral fucntion, Si (x)
thanks in advance

I am trying to gain some experience in maple coding, frankly I'm terrible so a tutor has kindly set me some tasks. He wants me to write a procedure for solving any tridiagonal system of equations. Here is his brief:
Write a procedure to solve a given tridiagonal system of equations. Use lists to input the coefficients and do NOT use matrices and/or Maple arrays. The procedure can then be called at every time step. This will also be more involved.
After a bit of research I know this is the starting matrix:
b1x1 + c1x2 = d1
a2x1 + b2x2 + c2x3 = d2

The following system of equations can be solved by Maple 9.5 and Maple 10, but either takes a long time in Maple 11 or else simply won't solve. Is anyone else experiencing problems with the solve command? Earlier I noticed that Maple 11 was returning duplicates in solutions, but this is more serious. We tried this system on Maple 9.5 and Maple 10, and it solves easily, but on two computers with Maple 11, in classic worksheet mode, minutes went by with no solution.
{2*a[2,6]*a[2,9]-2*a[2,8]*a[2,9], 2*a[1,5]*a[3,1]+2*a[1,7]*a[3,1], 2*a[2,6]*a[3,4]-2*a[2,8]*a[3,4], 2*a[1,5]*a[2,1]+2*a[1,7]*

Several weeks ago I submitted a request titled "Plot This! - Elliptic Integrals", which Dr. Robert Israel responded to with the following code which successfully plots the relationship of two variables, beta and k, over the range of interest.
> with(plots); Digits := 15;
> implicitplot(2*EllipticE(sin(beta), k)-EllipticF(sin(beta), k) = tan(beta)*sqrt(1-k^2*sin(beta)^2), k = 0 .. .99, beta = 3.5 .. 5.5, view = [0 .. 1, 3.5 .. 5.5]);
However, the plot indicates that for the range of k=0..0.99, beta is approximately equal to 4.77 radians (273 degrees), whereas the paper that I am researching indicates a value of beta equal to 257 degrees 28 minutes. I have attached worksheet that includes the commands provided by Dr. Israel for information.