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On the summability of formal power series solutions of $$q$$-difference equations. I. (Sur la sommabilité des séries entières solutions formelles d’une équation aux $$q$$-différences. I.) (French) Zbl 0913.39002
Summary: We give a $$q$$-analogous version of the Gevrey asymptotic and of the Borel summability respectively due to G. Watson and E. Borel and developed during the last fifteen years by J.-P. Ramis, Y. Sibuya$$\dots$$ The goal of these authors was the study of ordinary differential equations in the complex plane. In the same manner, our goal is the study of $$q$$-difference equations in the complex plane along the way indicated by G. D. Birkhoff and W. J. Trjitzinsky [Acta Math. 61, 1-38 (1933; Zbl 0007.21103)].
More precisely, we introduce a new notion of asymptoticality which we call $$q$$-Gevrey asymptotic expansions of order 1. This notion is well adapted to the class of $$q$$-Gevrey power series of order 1. Next, we define the class of $$Gq$$-summable power series of order 1 and give a characterization in terms of $$q$$-Borel-Laplace transforms. We show that every power series satisfying a linear analytic $$q$$-difference equation is $$Gq$$-summable of order 1 when the associated Newton polygon has a unic slope equal to 1. We shall study a generalization of this work when the Newton polygon is arbitrary in a later paper.

##### MSC:
 39A10 Additive difference equations 30B10 Power series (including lacunary series) in one complex variable 40A30 Convergence and divergence of series and sequences of functions
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