# DSolve only works with redefinition of functions?

Posted 2 months ago
413 Views
|
3 Replies
|
2 Total Likes
|
 Hello,I am trying to solve the following system of two coupled differential equations. sol1 = DSolve[ { a'[t] == - 2 I g (a[t] + Exp[- I 2 g t] * b[t]), b'[t] == 2 I g (b[t] + Exp[ I 2 g t] * a[t]), a == 0, b == 1 }, {a, b}, t] which does not work. And I do not understand why as it has an analytic solution. It is simple to see by substituting a[t],b[t] in the following way: a[t_] := Exp[-2 I t g] aa[t] b[t_] := Exp[ 2 I t g ] bb[t] sol1 = DSolve[ { a'[t] == - 2 I g (a[t] + Exp[- I 2 g t] * b[t]), b'[t] == 2 I g( b[t] + Exp[ I 2 g t] * a[t]), a== 0, b== 1 }, {aa, bb}, t] I do not understand, why one version works, while the other does not? Any hints would be appreciated. What did I miss? Answer
3 Replies
Sort By:
Posted 2 months ago
 Does none have any advise, or maybe just a guess/idea what I could research on to find out by myself, why one case is working and the other is not? Answer
Posted 2 months ago
 Marius,You should report this to technical support. It fails for me in version 12.2 but in a different version of Mathematica it solves properly (both give the same answer)  Answer
Posted 2 months ago
 Hi Neil,Thanks for your reply. Oh ok. That's kind of sad, because now I can't really learn from it. But I reported it to the technical support!Thanks for looking at it. Marius Answer