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Paras31

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0 years, 171 days
Hellenic Open University
Mathematician

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Teacher of Mathematics with a proven track record of working in education management. Proficient in Ease of Adaptation, Course Design, and Instructional Technology. Strong education professional with a Bachelor's degree with an emphasis in Mathematics from the University of Aegean. Currently, he is pursuing a Master's degree in Applied Mathematics at the Hellenic Open University, with a specific focus on Ordinary and Partial Differential equations. His enthusiasm lies in the application of mathematical models to real-world contexts, such as epidemiology and population growth. Aside from his passion for teaching, Athanasios enjoys football, basketball, and spending time with his dogs.

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These are questions asked by Paras31

Linearly implicit Euler method...

Paras31 130 Maple 2024
method ode euler
Yesterday at 6:42 AM
0 1

Hello,

I noticed that the Linearly Implicit Euler method (also known as the Semi-Implicit Euler method) is not available in Maple's built-in ODE solvers. This method is useful for stiff ODEs, where part of the function is treated implicitly (for the linear term) and part is treated explicitly (for the non-linear term).

I know that the Linearly Implicit Euler method is a specialized method that probably does not find enough widespread use to justify its inclusion as a standard feature in Maple, especially given Maple's focus on numerical methods such as Runge-Kutta methods and fully implicit methods for rigid equations.

I’m wondering:

  1. Why isn’t this method included in Maple’s standard set of numerical solvers?
  2. How can I implement this method in my own code in Maple to solve stiff ODEs?

Any guidance or examples of implementation would be greatly appreciated!

Thank you!

Linearly_Implicit_Method.pdf

Avoiding placeholders for symbolic diffe...

Paras31 130 Maple 2024
differentiation differential-equations
September 28 2024
2 1

I’m currently working on a Maple project involving the symbolic differentiation of a user-defined potential energy function, which I then use in a system of differential equations. To implement this, I've been using placeholders like 'Un' when taking derivatives to substitute later during numerical calculations.

While this approach using placeholders works, I find it cumbersome and would prefer a more straightforward way to handle this symbolic differentiation without having to rely on intermediate placeholders like 'Un'.

Does anyone know if there is a more elegant way in Maple to achieve this functionality?

Specific Requirements:

  • I want to symbolically differentiate the user-defined function W directly.
  • The goal is to use this derivative in a system of differential equations for numerical solving.

Any suggestions on simplifying this process would be much appreciated!

Thanks in advance.

restart

NULL
W := proc (Un) options operator, arrow; -(1/4)*(b*d-e*q)^2/(b^2*(e+b*Un^2))-(2*b*c*m^2+(1/4)*q^2)*Un^2/b+c*Un^4 end proc

proc (Un) options operator, arrow; -(1/4)*(b*d-e*q)^2/(b^2*(e+b*Un^2))-(2*b*c*m^2+(1/4)*q^2)*Un^2/b+c*Un^4 end proc

 (1)

 

 

diff(W(Un), Un)

(1/2)*(b*d-e*q)^2*Un/(b*(Un^2*b+e)^2)-2*(2*b*c*m^2+(1/4)*q^2)*Un/b+4*c*Un^3

 (2)

b := -0.3070816340e-3; c := .4461893869; d := 0.1142581922e-1; e := 0.7675000601e-3; q := -0.3704049149e-2; m := 1.423206983; plot(W(Un), Un = -10 .. 10, title = "Graph of Potential W for set 1", color = blue, axes = boxed)

  

with(plots); with(DEtools); delta := .5; b := -0.222159366e-3; c := 1.088046084; d := 0.1308858509e-2; e := 0.394423507e-3; q := -0.64844084e-3; m := 1.518466566; W := proc (Un) options operator, arrow; -(1/4)*(b*d-e*q)^2/(b^2*(e+b*Un^2))-(2*b*c*m^2+(1/4)*q^2)*Un^2/b+c*Un^4 end proc; Un_placeholder := 'Un'; Wprime := diff(W(Un_placeholder), Un_placeholder); sys := {diff(u(t), t) = v(t), diff(v(t), t) = -delta*v(t)+subs(Un_placeholder = u(t), Wprime)}; ics1 := {u(0) = 0.1e-1, v(0) = 0.1e-1}; sol := dsolve(`union`(sys, ics1), numeric, output = listprocedure); xrange := -0.10e-1 .. 0.11e-1; yrange := -0.3e-1 .. 0.3e-1; phase_plot := odeplot(sol, [u(t), v(t)], 0 .. 100, title = "Phase Plot (Velocity vs Displacement)", numpoints = 8000, color = red, labels = ["u(t)", "v(t)"], axes = boxed, labeldirections = [horizontal, vertical]); vectorfield_plot1 := fieldplot([v, -delta*v+subs(Un_placeholder = u, Wprime)], u = xrange, v = yrange, arrows = medium, color = blue, axes = boxed); display([vectorfield_plot1, phase_plot], title = "Combined Phase Plot and Vector Field", labels = ["u(t)", "v(t)"], axes = boxed)

  

NULL

Download proteins.mw

Differences in Domain Results Between so...

Paras31 130 Maple 2024
solve inequality
September 25 2024
1 1

I recently encountered an interesting issue when solving for the domain of a function in Maple using two different approaches, and I am curious about the differences in results between the following commands:

  1. domain := solve(0 < x and x <> 2, x);
  2. domain := solve({0 < x, x <> 2}, x);

I wonder if anyone could explain why Maple might treat these two syntaxes differently.

> 

restart
> 

``
> 

h := proc (x) options operator, arrow; ln(x)/(x-2) end proc

proc (x) options operator, arrow; ln(x)/(x-2) end proc

 (1)
> 

domain_ln := solve(x > 0, x)

RealRange(Open(0), infinity)

 (2)
> 

denom_undefined := solve(x-2 = 0, x)

2

 (3)
> 

domain := solve(`and`(x > 0, x <> 2), x)

RealRange(Open(0), infinity)

 (4)
> 

solve({x > 0, x <> 2}, x)

{2 < x}, {0 < x, x < 2}

 (5)
> 

``
> 

plot(h(x), x = 0 .. 10, discont = true, color = blue)

 
> 

``


 

Download domain.mw

Plotting intersection point of two equat...

Paras31 130 Maple 2024
syntax substitution pointplot
September 23 2024
1 0

Hello everyone,

I successfully plotted the intersection point of two linear equations using a matrix-based approach. Still, I’m facing an issue when trying to achieve the same result using the second method — solving the system symbolically and plotting without matrices.

The Matrix-Based Approach (Working): I used the following steps to plot both equations and mark the intersection point (solution). However, when I switch to solving the system symbolically without matrices, I can plot the two lines, but I'm unable to plot the intersection point correctly.

It seems that the symbolic solution isn't being properly converted to a numeric form for pointplot, even though I’m using evalf.

Any help would be greatly appreciated!

Download Linear_System.mw

Error in Solving System of ODEs: "System...

Paras31 130 Maple 2024
ode dsolve differential-equations
September 10 2024
1 23

I'm trying to solve a system of coupled differential equations numerically, but I'm getting the following error

Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations

The error occurs at the dsolve step, despite trying to ensure that all equations and conditions are in the correct form (sets/lists).

Could someone help me identify what I'm missing here?

Thanks in advance!

L := 200; K := 99; kappa := 1; omegaD := 1; beta := 1; delta := 0.5e-1; j := 2; tmax := 3000; h := L/(K+1); nsp := [`$`(-(1/2)*L+h*i, i = 0 .. L/h)]; km := nops(nsp); omegaD2 := h^2*omegaD^2; deltaHat := h*delta; a := 2; var := seq(x[i](t), i = 1 .. km); initialPositions := seq(x = a*sin(j*h*Pi*nsp[i]/L), i = 1 .. km); initialVelocities := seq((D(x[i]))(0) = 0, i = 2 .. km-1)

boundaryConditions := [x[1](t) = 0, x[km](t) = 0]

equations := seq(diff(x[n](t), t, t)-kappa*(x[n+1](t)-2*x[n](t)+x[n-1](t))+deltaHat*(diff(x[n](t), t))-omegaD2^2*(x[n](t)-beta*x[n](t)^3) = 0, n = 2 .. km-1)

sol := dsolve({equations, boundaryConditions, initialPositions, initialVelocities}, var, numeric, method = rkf45, range = 0 .. tmax)

Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations

  

NULL

Download dsolve_error.mw

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