<PAGE>

Exhibit 11(a)


 
                          Computervision Corporation
         Calculation of Shares Used in Determining Earnings Per Share
 For the Three and Nine Months Ended September 29, 1996 and September 28, 1997
                                (In Thousands)
<TABLE> 
<CAPTION> 
                                                               Three Months Ended                       Nine Months Ended
                                                       -----------------------------------      ----------------------------------
                                                       September 29,       September 28,        September 29,      September 28,
Primary Earnings Per Share                                  1996                1997                 1996              1997
--------------------------                             ---------------   ------------------     ---------------   ----------------
<S>                                                    <C>               <C>                    <C>               <C>
Weighted average number of common shares
    outstanding during the period                              63,418               63,701              63,228             63,614
Common stock equivalents                                        1,060                    0               1,554                  0
                                                       ---------------   ------------------     ---------------   ----------------
Total                                                          64,478               63,701              64,782             63,614
                                                       ---------------   ------------------     ---------------   ---------------
<CAPTION> 
                                                               Three Months Ended                       Nine Months Ended
                                                       -----------------------------------      ----------------------------------
                                                       September 29,       September 28,        September 29,      September 28,
Fully Diluted Earnings Per Share                            1996                1997                 1996              1997
--------------------------------                       ---------------   ------------------     ---------------   ----------------
<S>                                                    <C>               <C>                    <C>               <C>
Weighted average number of common shares
    outstanding during the period                              63,419               63,701              63,228             63,614
Common stock equivalents                                        1,441                    0               1,679                  0
                                                       ---------------   ------------------     ---------------   ----------------
Total                                                          64,860               63,701              64,907             63,614
                                                       ---------------   ------------------     ---------------   ----------------
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