Simultaneous P.D.E. problem Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)P.D.E question. Constant Dirichlet'e EnergyHelp needed in solving a differential equationUsing a multivariate chain rule to solve a partial differential equationA system of simultaneous equationseasy simultaneous equation, please solveFinding X or Y first in simultaneous equationSimultaneous equation involving reciprocalsHow do I proceed from here solving partial differential equation with boundary conditionsSolving quasilinear p.d.e. with method of charactersticsP.D.E. problem Jacobi's Method

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Simultaneous P.D.E. problem



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)P.D.E question. Constant Dirichlet'e EnergyHelp needed in solving a differential equationUsing a multivariate chain rule to solve a partial differential equationA system of simultaneous equationseasy simultaneous equation, please solveFinding X or Y first in simultaneous equationSimultaneous equation involving reciprocalsHow do I proceed from here solving partial differential equation with boundary conditionsSolving quasilinear p.d.e. with method of charactersticsP.D.E. problem Jacobi's Method










1












$begingroup$



Solve the following differential equation:
$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$




I have so far got
$x^2dx = y^2dy $ which implies that $(x-y)(x^2 +xy + y^2) = a$ ...(1)



Then $$fracdx+ dy(x-y) = fracdzz$$
Using the equation (1), I get
$frac1a (x^2+xy+y^2)(dx+dy) = fracdzz$



How do I proceed from this point? I could have solved this question easily if the third fraction in the given P.D.E. were
$fracdzz(x^2 - y^2)$ but I need help for this problem. Please help me out.










share|cite|improve this question











$endgroup$











  • $begingroup$
    This appeared in my assignment in the subject of differential equations. The question as given in it is: Solve the following differential equation: $fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2)$
    $endgroup$
    – Vaibhav Ramani
    Apr 3 at 15:06
















1












$begingroup$



Solve the following differential equation:
$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$




I have so far got
$x^2dx = y^2dy $ which implies that $(x-y)(x^2 +xy + y^2) = a$ ...(1)



Then $$fracdx+ dy(x-y) = fracdzz$$
Using the equation (1), I get
$frac1a (x^2+xy+y^2)(dx+dy) = fracdzz$



How do I proceed from this point? I could have solved this question easily if the third fraction in the given P.D.E. were
$fracdzz(x^2 - y^2)$ but I need help for this problem. Please help me out.










share|cite|improve this question











$endgroup$











  • $begingroup$
    This appeared in my assignment in the subject of differential equations. The question as given in it is: Solve the following differential equation: $fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2)$
    $endgroup$
    – Vaibhav Ramani
    Apr 3 at 15:06














1












1








1





$begingroup$



Solve the following differential equation:
$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$




I have so far got
$x^2dx = y^2dy $ which implies that $(x-y)(x^2 +xy + y^2) = a$ ...(1)



Then $$fracdx+ dy(x-y) = fracdzz$$
Using the equation (1), I get
$frac1a (x^2+xy+y^2)(dx+dy) = fracdzz$



How do I proceed from this point? I could have solved this question easily if the third fraction in the given P.D.E. were
$fracdzz(x^2 - y^2)$ but I need help for this problem. Please help me out.










share|cite|improve this question











$endgroup$





Solve the following differential equation:
$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$




I have so far got
$x^2dx = y^2dy $ which implies that $(x-y)(x^2 +xy + y^2) = a$ ...(1)



Then $$fracdx+ dy(x-y) = fracdzz$$
Using the equation (1), I get
$frac1a (x^2+xy+y^2)(dx+dy) = fracdzz$



How do I proceed from this point? I could have solved this question easily if the third fraction in the given P.D.E. were
$fracdzz(x^2 - y^2)$ but I need help for this problem. Please help me out.







pde systems-of-equations






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Apr 3 at 17:28









Harry49

8,90331346




8,90331346










asked Apr 2 at 9:44









Vaibhav RamaniVaibhav Ramani

164




164











  • $begingroup$
    This appeared in my assignment in the subject of differential equations. The question as given in it is: Solve the following differential equation: $fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2)$
    $endgroup$
    – Vaibhav Ramani
    Apr 3 at 15:06

















  • $begingroup$
    This appeared in my assignment in the subject of differential equations. The question as given in it is: Solve the following differential equation: $fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2)$
    $endgroup$
    – Vaibhav Ramani
    Apr 3 at 15:06
















$begingroup$
This appeared in my assignment in the subject of differential equations. The question as given in it is: Solve the following differential equation: $fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2)$
$endgroup$
– Vaibhav Ramani
Apr 3 at 15:06





$begingroup$
This appeared in my assignment in the subject of differential equations. The question as given in it is: Solve the following differential equation: $fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2)$
$endgroup$
– Vaibhav Ramani
Apr 3 at 15:06











1 Answer
1






active

oldest

votes


















1












$begingroup$

$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$
This system of ODEs might come from solving the PDE :
$$y^2(x-y)fracpartial zpartial x+x^2(x-y)fracpartial zpartial y=(x^2+y^2)z$$
A first characteristic equation comes from $fracdxy^2(x-y) = fracdyx^2(x-y) $ which solution is :
$$y^3-x^3=c_1$$
This is what you rightly found : your equation (1).



A second characteristic equation comes from $fracdxy^2(x-y) = fracdzz(x^2 + y^2)$
$$fracdzz=fracx^2+y^2y^2(x-y)dx$$
with $y=(c_1+x^3)^1/3$
$$fracdzz=fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1-x^3)^1/3)dx$$
$$z=c_2expleft(int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx right)$$
The difficulty is to integrate for a closed form. If we could do it we would have a function $I(c_1,x)$ such as :
$$I(c_1,x)=int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx $$
and a second characteristic equation would be :
$$z,exp(-Ileft(c_1,x right) )=c_2$$
$$z,exp(-I(y^3-x^3,x) )=c_2$$
General solution of the PDE expressed on implicit form $c_2=F(c_1)$ :
$$z=exp(I(y^3-x^3,x) ) Fleft(y^3-x^3 right)$$
where $F$ is an arbitrary function to be determined according to some conditions (not specified in the wording of the question).



Nevertheless the solution is not obtained on a closed form, due to the weird integral.






share|cite|improve this answer











$endgroup$












  • $begingroup$
    Thank you very much!
    $endgroup$
    – Vaibhav Ramani
    Apr 5 at 2:13











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1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









1












$begingroup$

$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$
This system of ODEs might come from solving the PDE :
$$y^2(x-y)fracpartial zpartial x+x^2(x-y)fracpartial zpartial y=(x^2+y^2)z$$
A first characteristic equation comes from $fracdxy^2(x-y) = fracdyx^2(x-y) $ which solution is :
$$y^3-x^3=c_1$$
This is what you rightly found : your equation (1).



A second characteristic equation comes from $fracdxy^2(x-y) = fracdzz(x^2 + y^2)$
$$fracdzz=fracx^2+y^2y^2(x-y)dx$$
with $y=(c_1+x^3)^1/3$
$$fracdzz=fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1-x^3)^1/3)dx$$
$$z=c_2expleft(int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx right)$$
The difficulty is to integrate for a closed form. If we could do it we would have a function $I(c_1,x)$ such as :
$$I(c_1,x)=int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx $$
and a second characteristic equation would be :
$$z,exp(-Ileft(c_1,x right) )=c_2$$
$$z,exp(-I(y^3-x^3,x) )=c_2$$
General solution of the PDE expressed on implicit form $c_2=F(c_1)$ :
$$z=exp(I(y^3-x^3,x) ) Fleft(y^3-x^3 right)$$
where $F$ is an arbitrary function to be determined according to some conditions (not specified in the wording of the question).



Nevertheless the solution is not obtained on a closed form, due to the weird integral.






share|cite|improve this answer











$endgroup$












  • $begingroup$
    Thank you very much!
    $endgroup$
    – Vaibhav Ramani
    Apr 5 at 2:13















1












$begingroup$

$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$
This system of ODEs might come from solving the PDE :
$$y^2(x-y)fracpartial zpartial x+x^2(x-y)fracpartial zpartial y=(x^2+y^2)z$$
A first characteristic equation comes from $fracdxy^2(x-y) = fracdyx^2(x-y) $ which solution is :
$$y^3-x^3=c_1$$
This is what you rightly found : your equation (1).



A second characteristic equation comes from $fracdxy^2(x-y) = fracdzz(x^2 + y^2)$
$$fracdzz=fracx^2+y^2y^2(x-y)dx$$
with $y=(c_1+x^3)^1/3$
$$fracdzz=fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1-x^3)^1/3)dx$$
$$z=c_2expleft(int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx right)$$
The difficulty is to integrate for a closed form. If we could do it we would have a function $I(c_1,x)$ such as :
$$I(c_1,x)=int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx $$
and a second characteristic equation would be :
$$z,exp(-Ileft(c_1,x right) )=c_2$$
$$z,exp(-I(y^3-x^3,x) )=c_2$$
General solution of the PDE expressed on implicit form $c_2=F(c_1)$ :
$$z=exp(I(y^3-x^3,x) ) Fleft(y^3-x^3 right)$$
where $F$ is an arbitrary function to be determined according to some conditions (not specified in the wording of the question).



Nevertheless the solution is not obtained on a closed form, due to the weird integral.






share|cite|improve this answer











$endgroup$












  • $begingroup$
    Thank you very much!
    $endgroup$
    – Vaibhav Ramani
    Apr 5 at 2:13













1












1








1





$begingroup$

$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$
This system of ODEs might come from solving the PDE :
$$y^2(x-y)fracpartial zpartial x+x^2(x-y)fracpartial zpartial y=(x^2+y^2)z$$
A first characteristic equation comes from $fracdxy^2(x-y) = fracdyx^2(x-y) $ which solution is :
$$y^3-x^3=c_1$$
This is what you rightly found : your equation (1).



A second characteristic equation comes from $fracdxy^2(x-y) = fracdzz(x^2 + y^2)$
$$fracdzz=fracx^2+y^2y^2(x-y)dx$$
with $y=(c_1+x^3)^1/3$
$$fracdzz=fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1-x^3)^1/3)dx$$
$$z=c_2expleft(int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx right)$$
The difficulty is to integrate for a closed form. If we could do it we would have a function $I(c_1,x)$ such as :
$$I(c_1,x)=int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx $$
and a second characteristic equation would be :
$$z,exp(-Ileft(c_1,x right) )=c_2$$
$$z,exp(-I(y^3-x^3,x) )=c_2$$
General solution of the PDE expressed on implicit form $c_2=F(c_1)$ :
$$z=exp(I(y^3-x^3,x) ) Fleft(y^3-x^3 right)$$
where $F$ is an arbitrary function to be determined according to some conditions (not specified in the wording of the question).



Nevertheless the solution is not obtained on a closed form, due to the weird integral.






share|cite|improve this answer











$endgroup$



$$ fracdxy^2(x-y) = fracdyx^2(x-y) = fracdzz(x^2 + y^2) $$
This system of ODEs might come from solving the PDE :
$$y^2(x-y)fracpartial zpartial x+x^2(x-y)fracpartial zpartial y=(x^2+y^2)z$$
A first characteristic equation comes from $fracdxy^2(x-y) = fracdyx^2(x-y) $ which solution is :
$$y^3-x^3=c_1$$
This is what you rightly found : your equation (1).



A second characteristic equation comes from $fracdxy^2(x-y) = fracdzz(x^2 + y^2)$
$$fracdzz=fracx^2+y^2y^2(x-y)dx$$
with $y=(c_1+x^3)^1/3$
$$fracdzz=fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1-x^3)^1/3)dx$$
$$z=c_2expleft(int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx right)$$
The difficulty is to integrate for a closed form. If we could do it we would have a function $I(c_1,x)$ such as :
$$I(c_1,x)=int fracx^2+ (c_1+x^3)^2/3 (c_1+x^3)^2/3(x-(c_1+x^3)^1/3)dx $$
and a second characteristic equation would be :
$$z,exp(-Ileft(c_1,x right) )=c_2$$
$$z,exp(-I(y^3-x^3,x) )=c_2$$
General solution of the PDE expressed on implicit form $c_2=F(c_1)$ :
$$z=exp(I(y^3-x^3,x) ) Fleft(y^3-x^3 right)$$
where $F$ is an arbitrary function to be determined according to some conditions (not specified in the wording of the question).



Nevertheless the solution is not obtained on a closed form, due to the weird integral.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Apr 5 at 5:52

























answered Apr 4 at 9:59









JJacquelinJJacquelin

45.8k21858




45.8k21858











  • $begingroup$
    Thank you very much!
    $endgroup$
    – Vaibhav Ramani
    Apr 5 at 2:13
















  • $begingroup$
    Thank you very much!
    $endgroup$
    – Vaibhav Ramani
    Apr 5 at 2:13















$begingroup$
Thank you very much!
$endgroup$
– Vaibhav Ramani
Apr 5 at 2:13




$begingroup$
Thank you very much!
$endgroup$
– Vaibhav Ramani
Apr 5 at 2:13

















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