## Linear Kovalevskian systems with time-dependent coefficients.(English)Zbl 0559.35011

For the linear Kovalevskian system $$U_ t=\sum^{n}_{h=1}A_ h(t)U_ x+B(t)U$$ on $$R^ n\times [0,T]$$ with $$U(x,0)=g(x)$$, and $$A_ h(t)$$, B(t) complex $$N\times N$$ matrices in $$L^ 1[0,T]$$, the Cauchy- Kovalevski theorem states that if g is holomorphic in the strip of $$C^ n:$$ $$\{$$ $$| Im z| <k\}$$, then the problem has a unique solution analytic in x and absolutely continuous in t, for any t with $$\sup_{1\leq h\leq n}\{\| A_ h(s)\| ds\}\leq k$$. This last inequality is an estimate of the time of existence of the solution. Several examples show that the estimate is too crude and motivate refined estimates which are derived in this paper.
Reviewer: E.Barron

### MSC:

 35F05 Linear first-order PDEs 35A10 Cauchy-Kovalevskaya theorems 35B05 Oscillation, zeros of solutions, mean value theorems, etc. in context of PDEs
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### References:

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