On the existence and uniqueness of solutions of non-linear differential equation system












0












$begingroup$


Are there theorems that could be applied to show the existence/uniqueness of solution of such system :



$$
(S) left { begin{aligned}
p''&= f_1(b) \
q'' &= f_2(x,p,q,b)\
q~~ &= f_3(x,p,b)
end{aligned}
right.
$$



where $f_1$, $f_2$ and $f_3$ are non linear functions ? and $p$, $b$ and $q$ are real and positive functions defined on a compact $[a,b] subset mathbb{R+}$ ?










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$endgroup$












  • $begingroup$
    Is the last line of $(S)$ supposed to be $q=...$?
    $endgroup$
    – Not Mike
    Dec 4 '18 at 17:11










  • $begingroup$
    Yes why ? it characterizes how q is a function of the other unknowns $p$ and $b$.
    $endgroup$
    – AlexC75
    Dec 4 '18 at 17:12








  • 1




    $begingroup$
    If or where the last equation can be solved for $b$ this is an index-1 DAE in semi-explicit form. The general theory of differential-algebraic equations applies, which gives here apart from said solvability no further restrictions.
    $endgroup$
    – LutzL
    Dec 4 '18 at 17:21
















0












$begingroup$


Are there theorems that could be applied to show the existence/uniqueness of solution of such system :



$$
(S) left { begin{aligned}
p''&= f_1(b) \
q'' &= f_2(x,p,q,b)\
q~~ &= f_3(x,p,b)
end{aligned}
right.
$$



where $f_1$, $f_2$ and $f_3$ are non linear functions ? and $p$, $b$ and $q$ are real and positive functions defined on a compact $[a,b] subset mathbb{R+}$ ?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Is the last line of $(S)$ supposed to be $q=...$?
    $endgroup$
    – Not Mike
    Dec 4 '18 at 17:11










  • $begingroup$
    Yes why ? it characterizes how q is a function of the other unknowns $p$ and $b$.
    $endgroup$
    – AlexC75
    Dec 4 '18 at 17:12








  • 1




    $begingroup$
    If or where the last equation can be solved for $b$ this is an index-1 DAE in semi-explicit form. The general theory of differential-algebraic equations applies, which gives here apart from said solvability no further restrictions.
    $endgroup$
    – LutzL
    Dec 4 '18 at 17:21














0












0








0





$begingroup$


Are there theorems that could be applied to show the existence/uniqueness of solution of such system :



$$
(S) left { begin{aligned}
p''&= f_1(b) \
q'' &= f_2(x,p,q,b)\
q~~ &= f_3(x,p,b)
end{aligned}
right.
$$



where $f_1$, $f_2$ and $f_3$ are non linear functions ? and $p$, $b$ and $q$ are real and positive functions defined on a compact $[a,b] subset mathbb{R+}$ ?










share|cite|improve this question











$endgroup$




Are there theorems that could be applied to show the existence/uniqueness of solution of such system :



$$
(S) left { begin{aligned}
p''&= f_1(b) \
q'' &= f_2(x,p,q,b)\
q~~ &= f_3(x,p,b)
end{aligned}
right.
$$



where $f_1$, $f_2$ and $f_3$ are non linear functions ? and $p$, $b$ and $q$ are real and positive functions defined on a compact $[a,b] subset mathbb{R+}$ ?







differential-equations nonlinear-system






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share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 4 '18 at 17:16









LutzL

56.7k42054




56.7k42054










asked Dec 4 '18 at 17:00









AlexC75AlexC75

216




216












  • $begingroup$
    Is the last line of $(S)$ supposed to be $q=...$?
    $endgroup$
    – Not Mike
    Dec 4 '18 at 17:11










  • $begingroup$
    Yes why ? it characterizes how q is a function of the other unknowns $p$ and $b$.
    $endgroup$
    – AlexC75
    Dec 4 '18 at 17:12








  • 1




    $begingroup$
    If or where the last equation can be solved for $b$ this is an index-1 DAE in semi-explicit form. The general theory of differential-algebraic equations applies, which gives here apart from said solvability no further restrictions.
    $endgroup$
    – LutzL
    Dec 4 '18 at 17:21


















  • $begingroup$
    Is the last line of $(S)$ supposed to be $q=...$?
    $endgroup$
    – Not Mike
    Dec 4 '18 at 17:11










  • $begingroup$
    Yes why ? it characterizes how q is a function of the other unknowns $p$ and $b$.
    $endgroup$
    – AlexC75
    Dec 4 '18 at 17:12








  • 1




    $begingroup$
    If or where the last equation can be solved for $b$ this is an index-1 DAE in semi-explicit form. The general theory of differential-algebraic equations applies, which gives here apart from said solvability no further restrictions.
    $endgroup$
    – LutzL
    Dec 4 '18 at 17:21
















$begingroup$
Is the last line of $(S)$ supposed to be $q=...$?
$endgroup$
– Not Mike
Dec 4 '18 at 17:11




$begingroup$
Is the last line of $(S)$ supposed to be $q=...$?
$endgroup$
– Not Mike
Dec 4 '18 at 17:11












$begingroup$
Yes why ? it characterizes how q is a function of the other unknowns $p$ and $b$.
$endgroup$
– AlexC75
Dec 4 '18 at 17:12






$begingroup$
Yes why ? it characterizes how q is a function of the other unknowns $p$ and $b$.
$endgroup$
– AlexC75
Dec 4 '18 at 17:12






1




1




$begingroup$
If or where the last equation can be solved for $b$ this is an index-1 DAE in semi-explicit form. The general theory of differential-algebraic equations applies, which gives here apart from said solvability no further restrictions.
$endgroup$
– LutzL
Dec 4 '18 at 17:21




$begingroup$
If or where the last equation can be solved for $b$ this is an index-1 DAE in semi-explicit form. The general theory of differential-algebraic equations applies, which gives here apart from said solvability no further restrictions.
$endgroup$
– LutzL
Dec 4 '18 at 17:21










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