Management excludes from our non-GAAP measures certain recurring items to facilitate its review of the comparability of our core operating performance on a period-to-period basis because such items are not related to our ongoing core operating performance as viewed by management. Management considers our core operating performance to be that which can be affected by our managers in any particular period through their management of the resources that affect our underlying revenue and profit generating operations during that period. Management uses this view of our operating performance for purposes of comparison with our business plan and individual operating budgets and allocation of resources. Additionally, when evaluating potential acquisitions, management excludes the items described above from its consideration of target performance and valuation. More specifically, management adjusts for the excluded items for the following reasons:

• Identified intangible assets consist primarily of purchased technology, backlog, trade names, and customer relationships. Amortization charges for our intangible assets can vary in frequency and amount due to the timing and magnitude of acquisition transactions. We consider our operating results without these charges when evaluating our core performance due to the variability. Generally, the most significant impact to inter-period comparability of our net income is in the first twelve months following an acquisition.
• Special charges may include expenses related to employee severance, certain litigation costs, acquisitions, excess facility costs, and other asset related charges. Special charges are incurred based on particular facts and circumstances and can vary in size and frequency. Restructuring costs included in special charges include costs incurred for employee terminations, including severance and benefits, driven by modification of business strategy or business emphasis. Litigation costs classified as special charges consist of professional service fees related to patent litigation involving us, EVE S.A., and Synopsys, Inc. These costs are included in special charges because of their unusual nature due to the significance in variability of timing and amount. Special charges are not ordinarily included in our annual operating plan and related budget due to unpredictability, driven in part by rapidly changing technology and the competitive environment in our industry. We therefore exclude them when evaluating our managers’ performance internally.
• Equity plan-related compensation expenses represent the fair value of all share-based payments to employees, including grants of employee stock options and restricted stock units, and purchases made as a result of our employee stock purchase plans. We do not consider equity plan-related compensation expense in evaluating our managers’ performance internally or our core operations in any given period.
• Interest expense attributable to amortization of the original issuance debt discount on convertible debt is excluded. Management does not consider this charge as a part of our core operating performance. We do not consider the amortization of the original issuance debt discount on convertible debt to be a direct cost of operations.
• Equity in earnings or losses of unconsolidated entities represents our equity in the net income (loss) of common stock investments accounted for under the equity method. The carrying amounts of our investments are adjusted for our share of earnings or losses of the investee. We report our equity in the earnings or losses of investments in other income, net (with the exception of our investment in Frontline as discussed below). The amounts are excluded from our non-GAAP results as we do not control the results of operations for the investments and we do not participate in regular and periodic operating activities; therefore, management does not consider these investments as a part of our core operating performance.
• The Company maintains a 50% interest in Frontline, a joint venture. We report our equity in the earnings or losses of Frontline within operating income. Although we do not exert control, we actively participate in regular and periodic activities such as budgeting, business planning, marketing and direction of research and development projects. Accordingly, we do not exclude our share of Frontline’s earnings or losses from our non-GAAP results as management considers the joint venture to be core to our operating performance.
• Income tax expense is adjusted by the amount of additional tax expense or benefit that we would accrue if we used non-GAAP results instead of GAAP results in the calculation of our tax liability, utilizing a normalized effective tax rate. Our GAAP tax rate for the year ended January 31, 2017 is 16.2%. Our normalized non-GAAP effective tax rate for the year ended January 31, 2017 is 19%. The normalized non-GAAP effective tax rate considers our global tax posture, including the weighted average tax rates applicable in the various jurisdictions in which we operate; approximates the elimination of the effects of non-recurring and period specific items which are often attributable to acquisition decisions and can vary in size and frequency; and considered our U.S. tax loss carryforwards and tax credits that were not previously recorded as a benefit in our financial statements. Our non-GAAP effective tax rate is subject to change over time for various reasons, including changes in geographic business mix, statutory tax rates, foreign re-investment expectations, and availability of U.S. tax loss carryforwards and tax credits that were not previously recorded as a benefit.
• Our agreement with the former owners of noncontrolling interests in one of our subsidiaries gave them a right to require us to purchase their interests for a price based on a formula defined in the agreement. Under GAAP, increases (or decreases to the extent they offset previous increases) in the calculated redemption value of the noncontrolling interests are recorded directly to retained earnings and therefore do not affect net income. However, as required by GAAP, these amounts are applied to increase or decrease the numerator in the calculation of basic and diluted earnings per share. In September 2015 we acquired the remaining noncontrolling interest in the subsidiary. The amount for the twelve months ended January 31, 2016 reflects the final adjustment of redemption value to the actual price we paid. Management does not consider fluctuations in the calculated redemption value of noncontrolling interests to be relevant to our core operating performance.