EXHIBIT (a)(1)(D)
                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
           (INCLUDING THE ASSOCIATED PREFERRED STOCK PURCHASE RIGHTS)
                                       OF

                               IKOS SYSTEMS, INC.
                                       AT
                              $11.00 NET PER SHARE
                                       BY

                              FRESNO CORPORATION,
                          A WHOLLY-OWNED SUBSIDIARY OF

                          MENTOR GRAPHICS CORPORATION

THE OFFER AND WITHDRAWAL RIGHTS EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON
            TUESDAY, JANUARY 8, 2002, UNLESS THE OFFER IS EXTENDED.

                                                                December 7, 2001
To Brokers, Dealers, Commercial Banks,
Trust Companies and Other Nominees:

     This letter relates to the offer being made by Mentor Graphics Corporation,
an Oregon corporation ("Mentor"), through Fresno Corporation, a Delaware
corporation ("Purchaser"), a wholly-owned subsidiary of Mentor, to purchase all
of the issued and outstanding common stock, par value $0.01 per share (the
"Shares"), of IKOS Systems, Inc., a Delaware corporation (the "Company"),
including the associated preferred stock purchase rights (the "Rights") issued
pursuant to the Amended and Restated Rights Agreement, dated January 22, 1999,
between the Company and Bank Boston, N.A., as amended (the "Rights Agreement"),
at a price of $11.00 per Share net to the seller in cash, without interest, upon
the terms and subject to the conditions set forth in the Purchaser's Offer to
Purchase dated December 7, 2001 and the related Letter of Transmittal (which
together, as amended, supplemented or otherwise modified from time to time,
constitute the "Offer").

     Unless the Rights Condition (as defined in the Offer to Purchase) is
satisfied, the Company's stockholders will be required to tender one Right for
each Share tendered in order to effect a valid tender of Shares in accordance
with the procedures set forth in "The Offer -- Procedures for Tendering Shares
and Rights" of the Offer to Purchase. Unless the Distribution Date (as defined
in the Offer to Purchase) occurs, a tender of Shares will also constitute a
tender of the associated Rights.

     The Offer is conditioned upon, among other things, the following:

     - That the Company's stockholders validly tender and do not withdraw prior
       to the expiration date of the Offer a number of Shares, including the
       associated Rights, representing, together with the Shares owned by
       Mentor, at least a majority of the total number of outstanding Shares on
       a fully diluted basis.

     - That Mentor is satisfied, in its sole discretion, that the Agreement and
       Plan of Merger and Reorganization dated July 2, 2001 among the Company,
       Synopsys, Inc. and Oak Merger Corporation (the "Synopsys Agreement") has
       been terminated in accordance with the terms of such agreement as in
       effect on the date of the Offer to Purchase or such other terms as may be
       satisfactory to Mentor in its sole discretion.

     - That the termination fee provision in the Synopsys Agreement has been
       invalidated or the obligations to pay any amounts pursuant to such
       provision have been terminated, without any termination fee, or any
       portion thereof, having been paid by the Company or any of its affiliates
       pursuant to the Synopsys Agreement.


     - That the board of directors of the Company redeems the Rights in
       accordance with the terms of such Rights as in effect at such time or
       Mentor is satisfied, in its sole discretion, that the Rights have been
       invalidated or are otherwise inapplicable to the Offer and the Proposed
       Merger of Purchaser with and into the Company (the "Proposed Merger").

     - That Mentor is satisfied, in its sole discretion, that the provisions of
       Section 203 of the Delaware General Corporation Law do not apply to or
       otherwise restrict the Offer and the Proposed Merger.

     - That the Company's stockholders do not approve the Synopsys Agreement.

     - That the Company has not entered into or effectuated any agreement or
       transaction with any person or entity having the effect of impairing
       Purchaser's ability to acquire the Company or otherwise diminishing the
       expected economic value to Mentor of the acquisition of the Company.

     - That any waiting periods under applicable antitrust laws have expired or
       have been terminated.

     For your information and for forwarding to your clients for whom you hold
Shares registered in your name or in the name of your nominee, we are enclosing
the following documents:

          1.  Offer to Purchase dated December 7, 2001;

          2.  Letter of Transmittal for your use and for the information of your
     clients (including Guidelines for Certification of Taxpayer Identification
     Number on Substitute Form W-9 providing information relating to backup
     federal income tax withholding);

          3.  Notice of Guaranteed Delivery to be used to accept the Offer if
     the Shares and all other required documents cannot be delivered to
     Wilmington Trust Company ("the Depositary") by the Expiration Date (as
     defined in the Offer to Purchase);

          4.  A form of letter which may be sent to your clients for whose
     accounts you hold Shares registered in your name or in the name of your
     nominee, with space provided for obtaining such clients' instructions with
     regard to the Offer; and

          5.  Return envelope addressed to the Depositary.

     WE URGE YOU TO CONTACT YOUR CLIENTS AS PROMPTLY AS POSSIBLE. THE OFFER AND
WITHDRAWAL RIGHTS EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON TUESDAY,
JANUARY 8, 2002, UNLESS THE OFFER IS EXTENDED.

     Purchaser will not pay any fees or commissions to any broker or dealer or
other person (other than the Information Agent or the Depositary as described in
the Offer to Purchase) for soliciting tenders of Shares and Rights pursuant to
the Offer. Purchaser will, however, upon request, reimburse brokers, dealers,
commercial banks and trust companies for reasonable and necessary costs and
expenses incurred by them in forwarding materials to their customers. Purchaser
will pay all stock transfer taxes applicable to its purchase of Shares and
Rights pursuant to the Offer, subject to Instruction 6 of the Letter of
Transmittal.

     In order to accept the Offer, a duly executed and properly completed Letter
of Transmittal and any required signature guarantees, or an Agent's Message (as
defined in the Offer to Purchase) in connection with a book-entry delivery of
Shares, and any other required documents, should be sent to the Depositary by
12:00 Midnight, New York City time, on Tuesday, January 8, 2002.

     Any inquiries you may have with respect to the Offer should be addressed
to, and additional copies of the enclosed materials may be obtained from, the
Information Agent or the undersigned at the addresses and telephone numbers set
forth on the back cover of the Offer to Purchase.

                                          Very truly yours,

                                          MENTOR GRAPHICS CORPORATION
                                          FRESNO CORPORATION

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     NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU
THE AGENT OF PURCHASER, MENTOR, THE INFORMATION AGENT OR THE DEPOSITARY, OR
AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR MAKE ANY STATEMENT ON
BEHALF OF ANY OF THEM IN CONNECTION WITH THE OFFER OTHER THAN THE DOCUMENTS
ENCLOSED HEREWITH AND THE STATEMENTS CONTAINED THEREIN.

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