Hi all,

I need to compute all roots of a polynomial equation for geometric reasons. I do want accuracy but more important is speedy calculations. I know fsolve works pretty well, but I process the polynomials on my own first. Does the roots command work better? What about solvetools. Any and all thoughts welcome.

Note I need to compute all roots.

While solving an exercise in class, I ran into the following interesting solution of a transcendental equation.  It was not intentionally designed to be like this.

restart;
eq := 2*exp(-2*t) + 4*t = 127:
fsolve(eq, t=0..infinity);
                         31.75000000

The solution looks like a rational number while it was expected to be transcendental.  Let's increase the number of digits:

Digits := 20:
fsolve(eq, t=0..infinity);
Digits := 10:
                     31.750000000000000000

Let's make it even more accurate:

Digits := 29:
fsolve(eq, t=0..infinity);
Digits := 10:
                 31.750000000000000000000000000

And even more:

Digits := 40:
fsolve(eq, t=0..infinity);
Digits := 10:
           31.74999999999999999999999999986778814353

Is there a deep reason why the solution is so close to being a rational or is it just a coincidence?

I want to estimate numerically the value of P (that is the probability that f exceeds the value 12 when x, y and z are uniformly distributed within the box [-Pi, Pi]³).

restart
f := sin(x)+7*sin(y)^2+0.1*z^4*sin(x);
Omega := [x, y, z] =~ [(-Pi..Pi)$3]:
                                2        4       
               sin(x) + 7 sin(y)  + 0.1 z  sin(x)


h := Heaviside(f-12):
P := Int(h, Omega);

Here is a simple Monte Carlo estimation of P.

f_MC  := x -> sin(x[1])+7*sin(x[2])^2+0.1*x[3]^4*sin(x[1]); 
h_MC  := x -> Heaviside(f_MC(x) - 12);
omega := -Pi, Pi;
                         
P_MC := proc(N)
  local Z := Statistics:-Sample(Uniform(omega), [N, 3]):
  local F := Vector(N, n -> h_MC(Z[n])):
  local K := add(F):
  local P := evalf(add(F)/N):
  local q := Statistics:-Quantile(Normal(0, 1), 0.005, numeric):
  local e := -q*sqrt(P*(1-P)/N):
  printf("A bilateral 99%% confidence interval that Prob(f > 12) is %1.3e +/- %1.2e\n", P, e);
end proc:

P_MC(10^6)
A bilateral 99% confidence interval that Prob(f > 12) is 1.643e-02 +/- 3.27e-04

I was hoping to get a value for P using  evalf/Int with some method.
But I didn't succeed with any of the methods for multiple integration:

• The following command returns 0 for n=1 and 2 and Int(h, Omega) if n >=3

  evalf( Int(h, Omega, 'epsilon=1e-n', 'method=_MonteCarlo') );
  

   

• And all my attempts with methods from the Cuba library have resulted in an unevaluated Int(h, Omega) integral. 
   

Could you help me to estimate P using  evalf/Int ?
TIA

Hi,
Can anyone tell me what's going wrong with int(Heaviside(f-1/2), x=0..1, y=0..1); ?
 

restart:

f := x*y:

JH := int(Heaviside(f-1/2), x=0..1, y=0..1);  #???
                               1
                               -
                               4

 JP := int(piecewise(x*y>1/2, 1, 0), x=0..1, y=0..1); 
                          1   1      
                          - - - ln(2)
                          2   2      

# integrate "1" over the domain where f > 1/2

S := solve(f=1/2, x):
JS := int(1, x=S..1, y=1/2..1);
                          1   1      
                          - - - ln(2)
                          2   2      

Thanks in advance
 

При использовании «объединения» нумерация не сохраняется. Непонятно, по каким алгоритмам «объединение» применяется к тому или иному месту. Почему sistema [1] не равно GRAN [1]? Как я могу это исправить?

PS Прошу прощения за грамматические ошибки, английский плохо знаю

1. mws
 

Скачать 1.mws

Initially I have a system of w(x,y,t) and f(x,y,t). I have a set of two partial differential equations with this system. Later on, the system is modified into w(x,y,t,z) andf(x,y,t,z) where x and z are related due to the presence of boundary layers. Because of this, the partial differential expressions with respect to x has to change.

For example, initially: diff(w(x,y,t),x)=diff(w(x,y,t),x)
Later on, when the system gets modified in the presence of boundary layers on application of chain rule: diff(w(x,y,t,z),x)=diff(w(x,y,t,z),x)+diff(w(x,y,t,z),z)*diff(z,x)

This change has to happen for all higher order derivatives of x. In my case, I have upto 4th order derivative in x. How do I achieve these changes in the expressions in Maple in an elegant manner?

Good day everyone. I need to calculate series of the function given above. But I can not find result. It writes "Error, (in series/function) improper op or subscript selector". How can I fix this error? Please help me.

The detailed file has been attached above.
 

Download function.mwfunction.mw

I want to create a random polynomial using randpoly() with coefficients in a given list A := [1,1,2,5,6].

For that, I need to create a function that works as rand(1..9) but that when called returns a random element of A instead of a random number between 1 and 9.

What I have tried so far is

r := rand(1..numelems(A))
A[r()]

However, that returns a random element of A, not a function that returns a random element of A.

I've also tried

rand(A(1..numelems(A)))

But that gives an error.

One way of solving this problem would be to find out how to create a `..` type with the desired elements, something that works as 1..9 but with the elements of A. But convert(A,`..`) doesn't work and the rest of the things I tried don't work either.

Hi,

 I can’t use my "Filled" command to simultaneously explore my 3 graphs

Thanks for ideas

PétalesGraphes.mw

Hi, I am new to MAPLE and trying to solve the given BVP using shooting method but after defining the expression in u0 and u1, the code didn't compute the numerical value, and so that the whole code won't run exactly.
Please help me out to figure out the problem. I am looking for the answer. (NOTE: I copied this code from the web and it run so fine with the example but when I changed it according to me, it give me errors.)
The code is given below:
Thanks


restart;
with(DEtools);
with(plots);
dpdexi := 2;
K := 0.2;
epsilon := 0.0001;
                       epsilon := 0.0001
ode1 := (diff(phi(eta), eta) + epsilon*K*diff(phi(eta), eta)^3)/(1 + epsilon*diff(phi(eta), eta)^2) = dpdexi*eta;
bc1 := phi(0) = 0, phi(1) = 0;
a := 0;
b := 1;
ic1 := bc1[1], D(phi)(a) = alpha;
constraint := lhs(bc1[2]) - rhs(bc1[2]);
constraint = 0;
a0 := 0;
u0 := eval(constraint, phi(b) = PHIb(eval({ic1, ode1}, alpha = a0), phi(eta), b));
a1 := 0.01;
u1 := eval(constraint, phi(b) = PHIb(eval({ic1, ode1}, alpha = a1), phi(eta), b));
while fnormal(u1 - u0) <> 0 do
    z := solve(u1 = (u1 - u0)*(a1 - x)/(a1 - a0), x);
    a0, a1 := a1, z;
    u0, u1 := u1, eval(constraint, u(b) = Ub(eval({ic1, ode1}, alpha = z), u(x), b));
end do;
alpha_opt1 := z;
shoot_sol1 := evalf(dsolve(eval({ic1, ode1}, alpha = alpha_opt1), u(x), implicit));
infolevel[dsolve] := 3;
exact_sol1 := combine(dsolve({bc1, ode1}, u(x)));
infolevel[dsolve] := 0;
plot([rhs(exact_sol1), rhs(shoot_sol1)], x = 0 .. 1, color = [BLACK, RED], thickness = [5, 2], legend = ['exact', 'shooting'], title = "Figure 17.3");
evalf(eval(rhs(shoot_sol1), x = 1));

Hi..

OK, so my real-life example is I have a 3m gap between the house and the garage which I want to hang a sunshade. 
The hanging point on the house is 2.6m high and on the garage 2.1m (above ground). 

I have a choice between 2 sun sails, and I want to know -approximately- what sag I can expect from each.

I realise this is not exactly the same as the hanging wire problem i posted before.. but it my attempt anyway. Can anyone improve?

Sails.mw

there is this ref

https://www.mapleprimes.com/questions/147809-Real-Solution-For-Catenary-Differential-Equation

hello how do i define new units of multiple units. so i am able to choose them inside the Choose Unit in the rigth side

because as you can see there are not an option to define this as Unit -> [J/(K*mol)]

instead i have the option to use [m^2*kg/(s^2*K*mol)]

because i seen that you can defijne and install new units i just dont know how to impliment it so they alway remember my new units without i am suposed to initialize it with a command at top of my script

ps i also dont know how to define my new unit an just run that command at top of my script either.

but it would be better if it is permanent installed

i ask because i have several other units that is trublesome in maple (being in chemistry, we dont always use SI units) so molar [M] is also some times trublesome

as mapleprime often ask if we can include code i will do that

write this formula

3/(2)*8.3144621*J*K^(-1)*mol^(-1)

and use the simplify command in the right side and see that the unit is

thx

Hi. following on from

https://www.mapleprimes.com/questions/232817-Solving-Hanging-Cable-#comment281577

Second case: unequal poles.

I tried to work with vv's solution, but I got a problem... the required formula is

y=10.85378553130*cosh(0.0921337534371039*x) - 10.85378553130

Uneven.mw

Hi,

I have been trying to duplicate a solution to Schrodinger Eq from a utube video...the presenter use Wolfram software to graph and 

animate the plot...I have working on this all day..I a new user (several months)..any help would be appreciated.

I am attaching a screenshot

Thanks 

Frank

I am attaching my Maple worksheet for reference 
 

Download Lec7QuantumWaveSE.mw
 

Download Lec7QuantumWaveSE.mw
 

Download Lec7QuantumWaveSE.mw

I am trying to plot a Runge-Kutta method for 1+ tsin(tx). When ever I try to do the plot data command an empty graph shows up. I noticed that some of my values from the algorithm did not calculate properly. How do I fix this problem? This is what I typed in for the calculations. 

f := (t, x) -> 1 + t*sin(x);
t[0] := 0;x[0] := 0;
h := 0.1;
 

for n to 20 do
    t[n] := n*h;
    m1 := f(t[n - 1], x[n - 1]);
    m2 := f(t[n - 1] + h/2, x[n - 1] + m1*h/2);
    m3 := f(t[n - 1] + h/2, x[n - 1] + m2*h/2);
    m4 := f(t[n - 1] + h, h*m3 + x[n - 1]);
    x[n] := x[n - 1] + h/6*(m1 + 2*m2 + 2*m3 + m4);
end;