Items tagged with laplace-transform

My question is: Use the laplace transform to solve the system.

dx/dt + d^2y/dt^2 = 5e^(2t)

dx/dt - x - dy/dt + y = 8e^(2t)

x(0) = 2, y(0) = 1, y'(0) = 1

What I've done in Maple:

with(inttrans);
with(DEtools);
eq5 := (diff(x(t), t)+diff(y(t), t$2) = 5*exp(2*t), t, s);

eq5s := laplace(%, t, s);

eq6 := (diff(x(t), t)-x-(diff(y(t), t))+y = 8*exp(2*t), t, s);

eq6s := laplace(%, t, s);

solve({eq5s, eq6s}, {laplace(x(t), t, s), laplace(y(t), t, s)});

subs({x(0) = 2, y(0) = 1, (D(y))(0) = 1}, %);

eq3 := invlaplace(%, s, t);

How do I simplify?  If you plug it into maple I come up with an answer that has x and y on each side.  I guess I'm just wondering how I can set them equal to each other to solve and get rid of the variable x and y.  I know answer is correct as I've also ran it through ODEtest.  Please help.

However you figure out getting rid of the variables I assume will help me also in solving the next problem:

Use the Laplace Transform to solve the system

dx/dt = 7x - y + 6z

dy/dt = -10x + 4y - 12z

dz/dt = -2x + y - z

x(0) = 5, y(0) = 7, z(0) = 2

I have attempted the second problem much like the first.  Thank you for your time.

Is Symbolic Laplace and Inverse Laplace transform possible on Maple? if Yes, how do I find the inverse laplace of this function 

Thanks.

I resolved the coefficients to a 2nd order diff eq of the form:ay''+by'+cy=f(t)

I have included the .mw file for convenience at the link at the bottom of the page.  I resolved the coefficients in 2 different ways & they do not concur.  The 1st approach used the LaPlace transform & partial fraction decomposition.  The coefficient results are given by equations # 14 & 15.  The 2nd approach used undetermined coefficients where I assumed the particular solution and then applied the initial conditions to resolve the coefficients pertaining to the homogeneous solution which are given in the results listed in equation #23.  Noted in the 1st case the coeff's are A3 & A4 and for the 2nd approach the coeff's are A1 & A2.  I have worked this numerous times & do not understand why they do not concur.  So I thought I should get some fresh eyes on the problem to find where I may have gone wrong.

Any new perspective will be greatly apprecieated.

I had trouble uploading the .mw file so I have included an alternative link to retrieve the file if the code contents is illegible or you cannot dowlad the file drectly from the weblink  Download coeffs_of_homogen_soln_discrepancy.mw.  You should be able to download from the alternative link below once you paste the link into your browser.  If you cannot & wish for me to provide the file in some other fashion respond with some specific instructions & I will attempt to get the file to you.

https://unl.box.com/s/dywe90wwpy0t4ilkuxshkivz2z26mud8

Thanks 4 any help you can provide.

Download coeffs_of_homogen_soln_discrepancy.mw

I would like to apply inverse Laplace transform to U(x,p), which is defined by

For simplicity with my calculations, I assumed p:=i*beta^2. That is why I have the following equation after applying Laplace transform

(beta=0 is not a pole, that is why I removed the last term in my calculations later. Because there is no contribution) where

Here p and beta are complex values, we can write Re(p)=-2*Re(beta)*Im(beta), Im(p)=(Re(beta))^2-(Im(beta))^2 due to p:=i*beta^2. I numerically compute the roots of h(beta), you can find the numerical values of beta (I assumed digits are 50 due to accuracy ) betap.mw

Finally, I would like to plot U(x,t) with the values t=0.8, lambda=1, L=10, k=1. For checking the figure give t=0 and observe that U(x,0)=0.

I am expecting the plot is more or less like the following figure

PS: I already tried to solve and plot the problem, but I could not find where I make a mistake. I  share the worksheet below. Thank you!

complexplot.mw

I am relatively inexperienced with Maple and would like to either be pointed in the right direction or shown a similar example to my problem for reference.

My problem is I need to write a programme using the below equations

d^2x/dt^2=ax+by

d^2y/dt^2=cx+by

I then have to use the below values to show my programme works

a=b=c=d=1

x(0)=1

Dx(0)=0

y(0)=0

Dy(0)=1

After proving it works I have to apply it to a mass spring system using realistic parameters. Using visual and analytical ways to show findings.

md^2x/dt^2=-kx-k(x-y)

md^2y/dt^2=-k(y-x)-ky

when x and y are the displacement from the equilibrium. Initially the masses are displaced from their equilibrium posistions and released so that

x(0)=a, y(0)=b, Dy(0)=Dx(0)=0

then repeat with different smaller calculations

Any help would be much appreciated

Thanks

What´s the error here??????

Solução do Sistema de EDO's por Transformada de Laplace

 

restart

with(inttrans):

eq1 := diff(x(t), t)+(2.2*x(t)*y(t)+0.5e-1*x(t)/(5+0.5e-1*t)) = 0;

diff(x(t), t)+2.2*x(t)*y(t)+0.5e-1*x(t)/(5+0.5e-1*t) = 0

(1)

eq2 := diff(y(t), t)+(2.2*x(t)*y(t)-(0.5e-1*(0.25e-1-y(t)))/(5+0.5e-1*t)) = 0;

diff(y(t), t)+2.2*x(t)*y(t)-0.5e-1*(0.25e-1-y(t))/(5+0.5e-1*t) = 0

(2)

eq3 := diff(z(t), t)-2.2*x(t)*y(t)+0.5e-1*z(t)/(5+0.5e-1*t) = 0;

diff(z(t), t)-2.2*x(t)*y(t)+0.5e-1*z(t)/(5+0.5e-1*t) = 0

(3)

EQ := [eq1, eq2, eq3]:

for i to 3 do La[i] := laplace(EQ[i], t, s) end do;

s*laplace(x(t), t, s)-1.*x(0.)+2.200000000*laplace(x(t)*y(t), t, s)+laplace(x(t)/(100.+t)^1., t, s) = 0.

 

-1.*y(0.)-0.2500000000e-1*(exp(100.*s))^1.*Ei(1., 100.*s)^1.+1.*s^1.*laplace(y(t), t, s)^1.+2.200000000*laplace(x(t)^1.*y(t)^1., t, s)+1.*laplace(y(t)^1./(100.+1.*t)^1., t, s) = 0.

 

s*laplace(z(t), t, s)-1.*z(0.)-2.200000000*laplace(x(t)*y(t), t, s)+laplace(z(t)/(100.+t)^1., t, s) = 0.

(4)

LL := subs({laplace(x(t), t, s) = X, laplace(y(t), t, s) = Y, laplace(z(t), t, s) = Z}, [La[1], La[2], La[3]]);

[s*X-1.*x(0.)+2.200000000*laplace(x(t)*y(t), t, s)+laplace(x(t)/(100.+t)^1., t, s) = 0., -1.*y(0.)-0.2500000000e-1*(exp(100.*s))^1.*Ei(1., 100.*s)^1.+1.*s^1.*Y^1.+2.200000000*laplace(x(t)*y(t), t, s)+1.*laplace(y(t)/(100.+t)^1., t, s) = 0., s*Z-1.*z(0.)-2.200000000*laplace(x(t)*y(t), t, s)+laplace(z(t)/(100.+t)^1., t, s) = 0.]

(5)

sol := solve(LL, [X, Y, Z]):

assign(sol):

SOLS[X, Y, Z]:

SOLT := map(invlaplace, [X, Y, Z], s, t);

[-2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))-1.*(int(x(_U1)/(100.+_U1), _U1 = 0. .. t))+x(0), -1.*(int(y(_U1)/(100.+_U1), _U1 = 0. .. t))-2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))+y(0)+0.2500000000e-1*ln(1.+0.1000000000e-1*t), 2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))-1.*(int(z(_U1)/(100.+_U1), _U1 = 0. .. t))+z(0)]

(6)

SOLTT := evalf(subs({x(0) = 0.5e-1, y(0) = 0, z(0) = 0}, SOLT));

[-2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))-1.*(int(x(_U1)/(100.+_U1), _U1 = 0. .. t))+0.5e-1, -1.*(int(y(_U1)/(100.+_U1), _U1 = 0. .. t))-2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))+0.2500000000e-1*ln(1.+0.1000000000e-1*t), 2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))-1.*(int(z(_U1)/(100.+_U1), _U1 = 0. .. t))]

(7)

xx := evalc(Re(SOLTT[1]));

-2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))-1.*(int(x(_U1)/(100.+_U1), _U1 = 0. .. t))+0.5e-1

(8)

yy := evalc(Re(SOLTT[2]));

0.2500000000e-1*ln(abs(1.+0.1000000000e-1*t))-1.*(int(y(_U1)/(100.+_U1), _U1 = 0. .. t))-2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))

(9)

zz := evalc(Re(SOLTT[3]));

2.200000000*(int(x(_U1)*y(_U1), _U1 = 0. .. t))-1.*(int(z(_U1)/(100.+_U1), _U1 = 0. .. t))

(10)

plot([xx, yy, zz], t = 0 .. 500, legend = [x, y, z]);

Warning, expecting only range variable t in expression -2.200000000*int(x(_U1)*y(_U1),_U1 = 0. .. t)-1.*int(x(_U1)/(100.+_U1),_U1 = 0. .. t)+.5e-1 to be plotted but found names [_U1, x, y]

 

 

NULL

NULL


Download laplace.mw

Warning, solving for expressions other than names or functions is not recommended.

is the warning I get every time I try to solve for solve(ode1 = ode2, theta/T)

Is there any way I can solve for an expression (i.eg theta/T)?

 

Furthermore I would like to have an answer on how I get to laplace transforms (ODE) with only "s" in the output, if I type like this:

laplace(J*(diff(theta(t), t, t...

Hello all,

 

 

As in title I am really bothered with result in floating number obtained from laplace(expr, t, s).

I have a target to laplace and the laplace() gives me result with floating numbers.

(ex. laplace(diff(diff(f(t),t), t), t, s) = laplace(s^2. * laplace(f(t), t, s) : the period after 2 is annoying)

 

How can I avoid or do some conversions to kill the periods?

 

I want to invlaplace the following complex expression that I call PQ.

>PQ:=(cosh((1/2)*eta*sqrt(C3^2+4*C1*s))*sqrt(C3^2+4*C1*s)+sinh((1/2)*eta*sqrt(C3^2+4*C1*s))*C3)*(cosh((1/2)*eta*C3)-sinh((1/2)*eta*C3))*(-cosh(C4)-sinh(C4)+s)/(s^2*(-sinh((1/2)*C3)+cosh((1/2)*C3))*(sinh((1/2)*sqrt(C3^2+4*C1*s))*C3+sqrt(C3^2+4*C1*s)*cosh((1/2)*sqrt(C3^2+4*C1*s))))

where C1 C3 C4 eta are constant .

Then I do like this

>invlaplace(PQ)

But I got

Good morning everybody,


I have to make the Inverse Laplace Transformation of a function which is too complicated and the only way I have is to make it from the points of the function (I can get a plot but maple cannot get the formal form of the function because it is just too big). Does a numerical method exist in maple which can make the Inversion only from the points of the function?

Thank you,

ssteve

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