View source for Autochem

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{{notability|Products|date=August 2013}}
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{{Infobox software
| name = AutoChem
| logo = AutoChem.png
| logo_size = x64px
| screenshot =
| caption = <!--This field appear with a screenshot only-->
| developer = David Lary
| latest_release_version = v8
| latest_release_date = 2005
| operating_system = [[Cross-platform]]{{which|date=August 2013}}
| genre = [[List of numerical analysis software|Technical computing]]
| license = [[Commercial software|Commercial]] [[proprietary software]]
| website = {{URL|http://www.science-softcon.de/autochem/index.html}}
}}

'''AutoChem''' is [[NASA]] release software{{clarify|date=August 2013}} that constitutes an automatic computer code generator and documenter for chemically reactive systems<ref>{{Cite web|url=http://www.nasatech.com/Briefs/Nov05/GSC_14862_1.html|title = AutoChem| date=November 2005 }}</ref> written by [[David Lary]] between 1993 and the present. It was designed  primarily for modeling [[atmospheric chemistry]], and in particular, for chemical [[data assimilation]].

The user selects a set of chemical species. AutoChem then searches [[chemical reaction]] databases for these species and automatically constructs the [[ordinary differential equations]] (ODE) that describe the chemical system. AutoChem symbolically [[Derivative|differentiates]] the time derivatives to give the [[Jacobian matrix]], and symbolically differentiates the Jacobian matrix to give the [[Hessian matrix]] and the adjoint. The Jacobian matrix is required by many [[algorithms]] that solve the [[ordinary differential equations]] numerically, particular when the ODEs are stiff. The Hessian matrix and the adjoint are required for four-dimensional variational data assimilation (4D-Var). AutoChem documents the whole process in a set of [[LaTeX]] and [[PDF]] files.

The reactions involving the user specified constituents are extracted by the first AutoChem preprocessor program called Pick. This subset of reactions is then used by the second AutoChem preprocessor program RoC (rate of change) to generate the time derivatives, Jacobian, and Hessian. Once the two preprocessor programs have run to completion all the [[Fortran 90]] code has been generated that is necessary for modeling and assimilating the kinetic processes.

A huge observational [[database]] of many different atmospheric constituents from a host of platforms are available from the AutoChem site.<ref>{{cite web | url=http://www.science-softcon.de/autochem/constituentobservationaldatabase.html | title=Data References }}</ref>

AutoChem has been used to perform long term chemical data assimilation of atmospheric chemistry. This assimilation was automatically documented by the AutoChem software and is available on line at CDACentral.<ref>{{cite web|url=http://www.cdacentral.info/ |access-date=2017-04-24 | title= Welcome to CDA Central |url-status=dead |archive-url=https://web.archive.org/web/20060717223237/http://www.cdacentral.info/ |archive-date=July 17, 2006 }}</ref> Data quality is always an issue for chemical data assimilation, in particular the presence of biases. To identify and understand the biases it is useful to compare observations using [[Probability density function|probability distribution function]]s. Such an analysis is available on line at PDFCentral which was designed for the validation of observations from the NASA [[Aura (satellite)|Aura satellite]].<ref>{{cite web|url=http://www.pdfcentral.info/ |archive-url=https://web.archive.org/web/20070223072036/http://www.pdfcentral.info/ |title=PDF Central |url-status=dead |archive-date=February 23, 2007 |access-date=2017-04-24 }}</ref>

==See also==
* [[Chemical kinetics]]
* [[CHEMKIN]]
* [[Cantera (software)|Cantera]]
* [[Chemical WorkBench]]
* [[Kinetic PreProcessor|Kinetic PreProcessor (KPP)]]
* [[SpeedCHEM]]

==References==
{{reflist}}

{{Chemistry software}}

[[Category:Computational chemistry software]]
[[Category:Chemical kinetics]]
[[Category:Environmental chemistry]]


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