## 120 Reputation

10 years, 138 days

## @Kitonum  thank you for your answe...

thank you for your answer, I have to use the Gauss–Legendre quadrature rule for EQ after transformation that you did, has the Maple command for this rule?

## @Kitonum  tnx my friend, I followe...

tnx my friend, I followed this command(unapply). thank you.

tnx for your answer, I know that but can you express f function in terms of zeta only? my goal is to express f function in terms of zeta only and no x in it.

## @Carl Love  Thank you so much, but...

Thank you so much, but this equation has several roots, how can I get the other roots?

## @tomleslie  thank you for this poi...

thank you for this point but that answer(

https://www.mapleprimes.com/questions/227667-Solve-PDE-With-RungeKutta-Method-And-Plot

) has been deleted!!!

## @tomleslie  I created the right PD...

I created the right PDE and attached again, and the boundary conditions are:

w(0,t)=0
wx(0,t)=0
wxx(L,t)=0
wxxx(L,t)=0

and the initial conditions are:

w(x,0)=0
wt(x,0)=0

PDE := 35139.16048*(diff(w(x, t), x, x, x, x))+98646.00937*(diff(w(x, t), t, t))-2771.636*(diff(w(x, t), x, x)) = 24883.20000

code.mw

## @Carl Love nothing, there isn't...

nothing, there aren't points for those states, you are right, in partial derivatives we always assume that the other variables are constant, thank you, you solved my problem.

## @Carl Love Diff(P,T)[V] is diff(P,T...

Diff(P,T)[V] is diff(P,T) when V is constant and Diff(P,V)[T] is diff(P,V) when T is constant, infact I want to obtain the diff(P,T) , diff(P,V) and diff(P,V,V) with this equation:

EQ := V^3-R*T*V^2/P-(B^2+P*B*R*T*sqrt(T)/(P-A))*V-A*B/(P*sqrt(T)) = 0;

•

## @Carl Love Diff(P,T)[V] is diff(P,T...

Diff(P,T)[V] is diff(P,T) when V is constant and Diff(P,V)[T] is diff(P,V) when T is constant, infact I want to obtain the diff(P,T) , diff(P,V) and diff(P,V,V) with this equation:

EQ := V^3-R*T*V^2/P-(B^2+P*B*R*T*sqrt(T)/(P-A))*V-A*B/(P*sqrt(T)) = 0;

tnx for your answer, but when I used the Directsearch command the Maple has this error: "Error, `DirectSearch` does not evaluate to a module", while I installed the Directsearch package. why?

## @Kitonum  Thank you so much my fri...

Thank you so much my friend, how can I solve it with simpson method?

with regards

## @acer that is my project and I must...

that is my project and I must solve it with code in maple or direct command in maple like ApproximateInt.

thank you so much for your answer, how can I solve these equations with numeric and stiff=true options?

case1:

eqs1:=diff(r[1](t), t, t)+.73732117*(diff(r[1](t), t))+1190.3671*r[1](t)-0.15306600e-2*V(t) = -0.45063508e-2*q(t)-0.13147485e-1*cos(23*t), 2.03*10^(-8)*(diff(V(t), t))+1.*10^(-6)*V(t)+0.15306600e-2*(diff(r[1](t), t)) = 0, diff(q(t), t, t)+(22.847947*(q(t)^2-1))*(diff(q(t), t))+5800.3185*q(t) = -5269.2857*(diff(r[1](t), t, t))-59.454546*cos(23*t);
ics1:=V(0) = 0, q(0) = 0, (D(q))(0) = 0, r[1](0) = 0, (D(r[1]))(0) = 0;

case2:
eqs2:=diff(r[2](t), t, t)+.41088522*(diff(r[2](t), t))+79778.138*r[2](t)-0.11624742e-1*V(t) = 0.21841836e-2*q(t)-0.50553548e-2*cos(23*t), 2.03*10^(-8)*(diff(V(t), t))+1.*10^(-6)*V(t)+0.15306600e-2*(diff(r[1](t), t))+0.11624742e-1*(diff(r[2](t), t)) = 0, diff(q(t), t, t)+(22.847947*(q(t)^2-1))*(diff(q(t), t))+5800.3185*q(t) = -5269.2857*(diff(r[1](t), t, t))+2553.9707*(diff(r[2](t), t, t))-59.454546*cos(23*t);
ics2:=V(0) = 0, q(0) = 0, (D(q))(0) = 0, r[2](0) = 0, (D(r[2]))(0) = 0;

## @acer  Hi again, I edited my equat...

Hi again, I edited my equations and initial conditions, now i want to plot V(t) in terms of U0 in t=1s. tnx

eq1:=diff(r[1](t), t, t)+(.3754075596+.3045306134*U[0])*(diff(r[1](t), t))+740.0274933*r[1](t)-0.1181114312e-2*V(t) = -0.5234785518e-2*U[0]^2*q(t):
eq2:=2.030000000*10^(-8)*(diff(V(t), t))+4.065040650*10^(-7)*V(t)+0.1181114312e-2*(diff(r[1](t), t)) = 0:
eq3:=diff(q(t), t, t)-4.997988315*U[0]*(diff(q(t), t))+277.5543022*U[0]^2*q(t) = 0:
ics := V(0) = 0, q(0) = 0.1e-3, (D(q))(0) = 0, r[1](0) = 0, (D(r[1]))(0) = 0

## @acer  tnx for reply, forgive ...

tnx for reply, forgive me for this wrong, the value A=1 and I just obtain r1(t), V(t) , q(t) in terms of U0, ignore the problem plot. I just need solve the ODEs in terms of U0. tnx.

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