UNITED STATES

OMB APPROVAL

SECURITIES AND EXCHANGE COMMISSION

OMB Number:
3235-0145

Washington, D.C. 20549

Expires:
December 31, 2005

SCHEDULE 13G

Estimated average burden hours per response. . 11

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Rule 13d-1(b)

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Rule 13d-1(c)

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Rule 13d-1(d)

CUSIP No.  045327103

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
The TCW Group, Inc., on behalf of the TCW Business Unit

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

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(b)

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3.

SEC Use Only

4.

Citizenship or Place of Organization
Nevada corporation

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
-0-

6.

Shared Voting Power
2,486,751

7.

Sole Dispositive Power
-0-

8.

Shared Dispositive Power
2,649,031

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,649,031

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
6.5%

12.

Type of Reporting Person (See Instructions)
HC/CO

Item 1.

(a)

Name of Issuer
Aspen Technology, Inc.

(b)

Address of Issuer’s Principal Executive Offices
Ten Canal Park
Cambridge, MA 02141

Item 2.

(a)

Name of Person Filing
The TCW Group, Inc., on behalf of the TCW Business Unit

(b)

Address of Principal Business Office or, if none, Residence
865 South Figueroa Street
Los Angeles, CA 90017

(c)

Citizenship
(Nevada Corporation)

(d)

Title of Class of Securities
Common Stock

(e)

CUSIP Number
045327103

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

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Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

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Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e)

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An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

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An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

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A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

o

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

o

Group, in accordance with §240.13d-1(b)(1)(ii)(J).

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

The TCW Group, Inc., on behalf of the Business Unit ***

(a)

Amount beneficially owned:   
2,649,031

(b)

Percent of class:   
6.5%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   
none.

(ii)

Shared power to vote or to direct the vote    
2,486,751

(iii)

Sole power to dispose or to direct the disposition of   
none.

(iv)

Shared power to dispose or to direct the disposition of   
2,649,031

**           The filing of this Schedule 13G shall not be construed as an admission that the reporting person or any of its affiliates is, for the purposes of Section 13(d) or 13(g) of the Securities Exchange Act of 1934, the beneficial owner of any securities covered by this Schedule 13G.  In addition, the filing of this Schedule 13G shall not be construed as an admission that the reporting person or any of its affiliates is the beneficial owner of any securities covered by this Schedule 13G for any other purposes than Section 13(d) of the Securities Exchange Act of 1934.

***         See Exhibit A

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   o.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

Various persons other than as described in Item 4 have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Common Stock of Aspen Technology, Inc.

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

See Exhibit A.

Item 8.

Identification and Classification of Members of the Group

Not applicable.  See Exhibit A.

Item 9.

Notice of Dissolution of Group

Not applicable.

Item 10.

Certification

Because this statement is filed pursuant to Rule 13d﷓1(b), the following certification is included:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

Dated this 9th day of March, 2004.

The TCW Group, Inc., on behalf of the TCW Business Unit

By:

/s/ Linda D. Barker

Linda D. Barker
Authorized Signatory