(a) General rule. -- For purposes of the tax imposed by this article, a taxpayer's taxable year shall be the same as the taxpayer's taxable year for federal income tax purposes.

(b) Change of taxable year. -- If a taxpayer's taxable year is changed for federal income tax purposes, the taxpayer's taxable year for purposes of this article shall be similarly changed. The taxpayer shall provide a copy of the authorization for such change from the Internal Revenue Service, with its return for the taxable year filed under this article.

(c) Methods of accounting.
(1) Same as federal. -- A taxpayer's method of accounting under this article shall be the same as the taxpayer's method of accounting for federal income tax purposes. In the absence of any method of accounting for federal income tax purposes, the accrual method of accounting shall be used unless the tax commissioner, in writing, consents to use of another method.

(2) Change of accounting methods. -- If a taxpayer's method of accounting is changed for federal income tax purposes, his method of accounting for purposes of this article shall similarly be changed. The taxpayer shall provide a copy of the authorization for such change from the Internal Revenue Service, with its return for the taxable year filed under this article.