GCAM User Guide

Table Of Contents

1. Introduction

2. Quickstart

3. GCAM User’s Guide

• Configuration File
• GCAM Batch file
• Target finder mode
• ModelInterface
• Controlling the level of XML DB Output

1.Introduction

This document provides information on download and get running the GCAM model. To download GCAM you can follow the Download GCAM link in the upper right had corner. Users should find the GCAM version 5.1 release. There will be a few files available for download:

• gcam-v5.1-Mac-Release-Package.zip contains the GCAM executable, supporting libraries, the ModelInterface, and input XML files for the Mac OS X platform. Note for most Mac users this is typically the only package required.
• gcam-v5.1-Windows-Release-Package.zip contains the GCAM executable, supporting libraries, the ModelInterface, and input XML files for the Windows platform. Note for most Windows users this is typically the only package required.
• Source code (in zip or tar.gz format). This is the core of the release and contains all model source code and data processing scripts. Generally only needed if you need to compile the source code from scratch. Users who will need to maintain changes to source code and/or data processing code for an extended period of time should strongly consider checking out the repository with Git instead.

The following instructions for users who want to use the pre-built GCAM executable and XML input files. For instructions on compiling your own GCAM executable see GCAM Compile Instructions. For instructions on how to run the gcamdata R package to rebuild the XML input files from scratch see Running the GCAM Data System. Once built these users can proceed from the Quickstart guide.

To start users should download and unpack the Release Package appropriate for their platform to a location of their choosing. Throughout this document that location will be referred to as <GCAM Workspace>.

The rest of this user’s guide is divided into two parts. First a GCAM “quickstart” guide with basic instructions on running GCAM and viewing results, followed by a more detailed GCAM User’s Guide.

2. GCAM Quickstart

This section provides a brief introduction on how to use the GCAM Model and view model data using the GCAM model interface. The instructions in this Quickstart guide should work with a GCAM distribution release that has been downloaded and uncompressed to your local machine.

Warning: For GCAM 5.1 computational requirements have increased significantly. A GCAM model simulation will utilize over 8 GB of system RAM and storing the full results of the simulation will take around 2 GB of disk space per scenario.

2.1. Running a reference case scenario

GCAM requires a valid configuration.xml file be present in the exe directory of the GCAM workspace. You can run a reference scenario by copying the configuration_ref.xml that is provided in the distribution and renaming it to configuration.xml. The configuration file is descried in more detail in the User’s Guide section, and should not need to be modified in order to run a reference case scenario. The User’s Guide describes how to create additional scenarios.

A log_conf.xml file is also needed, but this file is provided in the release package and should therefore already be present in the exe directory.

In order to run GCAM double click on the run-gcam executable script or run the executable from the command line. You should see log messages scroll up the screen as GCAM reads in xml files and begins solving each model period. Log information for each run can be found in exe/logs/main_log.txt.

After a successful model run the log file will end with the following text (depending on your set-up and platform, you might also see this on your screen):

Starting output to XML Database.
Data Readin, Model Run & Write Time: 1273.42 seconds. 
Model run completed.
Model exiting successfully.

2.1.1 Common failures

The most common failure to run GCAM when double clicking the run-gcam executable script typically relate to Java. Dealing with Java differs depending on your system.

2.1.1.1 Windows

If a user sees a message similar to any of the following:

• Unable to locate jvm.dll
• A 64-bit Java is required to run GCAM
• Or sometimes a generic message about the application is unable to start correctly (referencing some memory address)

The most likely case is that the run-gcam.bat script was unable to detect the correct version of GCAM to use. Either there is no 64-bit version of Java installed or both a 32-bit and 64-bit is installed and it didn’t choose the right one. In either case you should edit run-gcam.bat and update the JAVA_HOME manually to point to the correct location and delete the REM before the SET:

REM Users may set the following location to the appropriate Java Runtime installation location
REM instead of trying to detect the appropriate location.  This may be necessary if the default
REM Java version is the 32-bit runtime.
REM SET JAVA_HOME=C:\Program Files\Java\jre1.8.0_101

Another common problem on Windows is GCAM also relies on the Microsoft Visual Studio 2015 Redistributable 64-bit package be installed as well. Although the error message in this situation tends to be more reliable and descriptive.

2.1.1.2 Mac

On the Mac a missing Java usually prompts an install of “legacy Java” from Apple. Note this install is no longer supported by GCAM. Instead users will need to install the Java Developer Kit from Oracle version 1.7 or newer. The processes is a little bit more involved so users should follow the same instructions for setting up Java when compiling GCAM.

2.1.1.2.1 Troubleshooting Java on Mac

The<GCAM Workspace>/exe/run-gcam.commandscript attempts to put a symbolic link into the libs/java directory that points to the location of the necessary java libraries (e.g., libjvm.dylib).

If, when attempting to run GCAM, the libraries are not found, you will get an error message of: dyld: Library not loaded: @rpath/libjvm.dylib. In this case the problem may be that the symlink is not actually pointing to the directory that contains the needed library. This can occur if the run-gcam.commandscript gets out of sync with the java version (e.g. using an older version of GCAM or if java is updated).

To fix this, use ls -l or readlink within terminal to resolve the symlink path. If the path is incorrect, then create a new symlink that points to the java sdk directory that contains the libjvm.dylib library (please see Java when compiling GCAM for details on how to do this).

2.2 Viewing Model Results

Comprehensive model output from each scenario is stored in an XML database. (Note that the current BaseX database is not compatible with older versions of GCAM and the GCAM model interface that use the .dbxml format.)

To view model output open the ModelInterface application. This multi-platform application is written in java and requires that java be installed on your machine.

Select Open from the Model Interface File menu and then select DB Open from the sub-menu. The default setting is that the XML database is located in the Output subdirectory and is called database_basexdb. Select database_basexdb and you should see the following on your screen.

Note as of GCAM 4.4 the ModelInterface package on the Mac may prompt you to select your query file if it can not locate it. This file is typically located in <GCAM Workspace>/output/queries/Main_queries.xml.

Figure UG-1: Screenshot of GCAM ModelInterface after an XML database has been opened, but before any queries have been run.

To view data select one or more scenarios, one or more regions, and one or more queries. The “Run Query” button will become available once one of each of these elements has been selected. Press this button and model output will appear as shown below:

Figure UG-2: Screenshot of GCAM ModelInterface after a query has been run.

A tabular data display will appear on the left and a simple graphical output will appear on the right. If multiple queries were selected, these will open in different tabs.

Sorting: You can sort results in the Model Interface tables by clicking on the table heading. You can add secondary sorting by holding ctrl while click another column heading.

Copying Data: You can copy the table to Excel by selecting copy from the file menu and pasting it to a worksheet. Column labels will not copy. An output table can also be directly dragged to an Excel worksheet by clicking on the output tab and dragging to an open Excel worksheet. Graphs will not be copied, only data.

3. GCAM User’s Guide

This user’s guide contains the following sections:

• Configuration File
• GCAM Batch file
• Target finder mode
• ModelInterface
• Controlling the level of XML DB Output

3.1 Configuration File

The configuration file directs the GCAM executable as to what files to read in and allows the user to set various runtime and output options. A configuration file must always be present for GCAM run. The configuration file is divided into following sections:

3.1.1 Scenario Components

The configuration_ref.xml file distributed with GCAM contains the list of input files that define the reference scenario for that GCAM release. Do not modify any of the original scenario component files. If you wish to make a change, make a copy of the file and modify the copy.

A common method of modifying a scenario is to add on additional components at the end of the list of scenario component files. Scenario components are read in order, and later data supersedes earlier data. A climate policy, for example, can be defined by adding a climate policy component. Examples of climate policy components can be found in the input/policy folder of the GCAM distribution.

For running multiple scenarios, Batch Mode is often more convenient.

3.1.2 <Files> Input Options

The following table summarizes the options available under the <Files> section of the configuration file. Note that for output files the write-output attribute is used to enable/disable output. The append-scenario-name attribute can be used to instruct GCAM to append the scenario name to the specified filename. See configuration_ref.xml for examples.

3.1.3 <Strings> Input Options

The following table summarizes the options available under the <Strings> section of the configuration file. These options should be strings, specified without quotes.

3.1.4 <Bools> Input Options

The following table summarizes the options available under the <Bools> section of the configuration file. These values should be specified as either 1 or 0.

3.1.5 <Ints> Input Options

The following table summarizes the options available under the <Ints> section of the configuration file. These values should be specified as integers.

3.2 GCAM Batch Mode

If running multiple scenarios, GCAM can also be run in Batch mode, in which a batch input file contains user-specified sets of add-on components that can be used to define multiple scenarios, which will then will all be run. In order to run in batch mode the BatchMode bool(ean) setting in the configuration file must be set to 1, and a batch input file must be specified as BatchFileName under <Files>.

The Batch file has the following format:

<BatchRunner>
	<ComponentSet name="Policy scenarios">
		<FileSet name="_set1">
		</FileSet>
		<FileSet name="_tax">
			<Value name="ctax">../input/policy/carbon_tax.xml</Value>
		</FileSet>
	</ComponentSet>
</BatchRunner>

The XML files within each FileSet block will be read in after the ScenarioComponents in the configuration file and then run. The scenario name of the run will be the name of each FileSet appended to the scenarioName in the configuration file.

If there are multiple ComponentSet blocks, then all permutations of FileSets within each ComponentSet will be run.

Note that there is also a batch functionality within the ModelInterface, which has a different format.

3.3 Target finder

Enabling this mode for running GCAM involves specifying a policy target file and enabling find-path. When running the target finder, as is the case when running any policy, users should start from the configuration_policy.xml to ensure the market structures are properly set up. When run in this mode GCAM will run a scenario several times to find the optimal path to satisfy the configured climate goal. Running GCAM in such a mode can take quite a bit of time, one option to speed this up is to provide a good initial-price-guess as documented below. Example policy target files are supplied in input/policy and are self documented:

<policy-target-runner name="forcing_4p5">
    <!-- tax-name | default: CO2 | The market name to change the price on --> 
	<tax-name>CO2</tax-name> 

    <!-- target-value | no default | The target value such as concentration 
         or forcing.
     -->
    <target-value>4.5</target-value>

    <!-- target-tolerance | default: 0.01 | The solution tolerance -->
    <target-tolerance>0.005</target-tolerance> 

    <!-- path-discount-rate | default: 0.05 | The hotelling rate -->
    <path-discount-rate>0.05</path-discount-rate>

    <!-- max-iterations | default: 100 | The maximum  number of attempts to
         solve any given period.
     -->
     <max-iterations>100</max-iterations>

    <!-- target-type | default: concentration | The climate parameter which
         we are targeting.  The available ones are:
            concentration | CO2 (or possibly other gasses via the configuration
                            string: concentration-target-gas)
            forcing | Total radiative forcing
            stabilization | Stabilize CO2 (or possibly other gasses via the
                           configuration string: concentration-target-gas)
                           with disregards to what that concentration might be
            kyoto-forcing | Radiative forcing from Kyoto GHGs only
            rcp-forcing | Radiative forcing using the RCP definition
            temperature | Global mean temperature
            cumulative-emissions | Reach a cumulative emission goal for CO2
                                   emissions (or possibly other gasses via the
                                   configuration string: cumulative-target-gas)
     -->
    <target-type>forcing</target-type>

    <!-- first-tax-year | default: 2020 | The first year to start a tax in -->
    <first-tax-year>2020</first-tax-year>

    <!-- initial-tax-guess | default: 5 | The first tax value to try, if a user
                                          can provide a good initial guess it may
                                          cut down on the total number of iterations
                                          significantly.
     -->
    <initial-tax-guess>5.0</initial-tax-guess>

    <!-- forward-look | default: 0 | Allow forward looking behavior by skipping
         this many periods.
     -->
    <forward-look>1</forward-look>

    <!-- stabilization | This is the default behavior is to stabilize the target
         overshoot year="2100" | Allow for an overshoot to hit in the target in
                                 given year.  If the year is not provided the 
                                 last model year will be assumed.  If it is 
                                 provided and before the last model year then 
                                 it will have to stay on target after that year.
     --> 
     <stabilization />

    <!-- max-tax | default: 4999 | Set a maximum tax to try in any given period
                                   to avoid extremely large taxes for which GCAM
                                   may have trouble solving.  Note that it may
                                   be possible the algorithm finds a solution
                                   with tax values capped at max-target for some
                                   years in which case the user should increase
                                   the max-tax.  If the actual solution price
                                   lies above max-tax the algorithm will fail.
     -->
    <max-tax>4999</max-tax>
</policy-target-runner>

Note that target finder runs can also be configured in Batch mode. In this case you should leave the find-path bool to 0. Note the policy-target-file are specified in their own section, and <single-scenario-runner /> indicates to run a permutation with no target finding, e.g. the reference scenario:

<BatchRunner>
    <ComponentSet name="Policy scenarios">
        <FileSet name="FFICT_">
            <Value name="land-policy">../input/policy/global_ffict.xml</Value>
        </FileSet>
        <FileSet name="UCT_">
            <Value name="land-policy">../input/policy/global_uct.xml</Value>
        </FileSet>
    </ComponentSet>
    <runner-set name="policy-target-runner">
        <Value name="6p0target">../input/policy/forcing_target_3p7.xml</Value>
        <Value name="4p5target">../input/policy/forcing_target_4p5.xml</Value>
        <Value name="2p6target">../input/policy/forcing_target_2p6_overshoot.xml</Value>
        <single-scenario-runner />
    </runner-set>
</BatchRunner>

3.4 ModelInterface

The model interface is a GCAM tool to view GCAM results from the BaseX XML database or convert CSV files to XML. You may find a copy at the top level of your release package and can be run by double clicking the ModelInterface.jar (on Mac this will be ModelInterface.app). This section will focus mainly on viewing results. It can be used in an interactive mode or users can set up batch query files to automate dumping results to CSV or XLS.

Note as of GCAM 4.4 the ModelInterface package on the Mac will by default save the model_interface.properties file in your home directory. You can change this by:

• Right click on the ModelInteface.app and select “Show Package Contents”
• Edit Contents/Info.plist (using TextEdit should be sufficient)
• Change the following <string> to an appropriate location, note you must use absolute paths.

<key>WorkingDirectory</key>
<string>$USER_HOME</string>

3.4.1 Interactive Mode

Please see the Quick Start section for the basics on how to open an database and run queries. The Scenarios and Regions sections get populated automatically from the GCAM results that are stored in the database. The Queries are loaded from a query file. You can check the model_interface.properties file which is located in the folder as the ModelInterface.jar or if using the ModelInterface.app on the Mac in your home directory:

<entry key="queryFile">../output/queries/Main_queries.xml</entry>

Note if the query file is not found the ModelInterface will ask you to select a new one. Each query is represented in it’s own XML syntax such as:

<emissionsQueryBuilder title="GHG emissions by region">
    <axis1 name="GHG">GHG</axis1>
    <axis2 name="Year">emissions</axis2>
    <xPath buildList="true" dataName="emissions" group="false" sumAll="false">*[@type = 'sector' (:collapse:) or @type = 'resource' (: collapse :)]//*[@type = 'GHG']/emissions/node()</xPath>
    <comments/>
</emissionsQueryBuilder>

This XML can be copied directly out of the ModelInterface by using Ctrl-C (or CMD-C on Mac) and pasted back into the Model Interface or as text elsewhere such as email. Similarly the XML text can be copied out of an email and pasted back into the Model Interface using Ctrl-V (or CMD-V on Mac). This is a handy short cut for sharing or editing queries. You will notice when queries are modified a * appears at the root of the queries. You can choose to File -> Save to update the underlying query file or use File -> Save As to save and switch to a new query file.

3.4.2 ModelInterface Batch Modes

When doing scenario analysis on GCAM results it is often very useful to predefine the set of queries you would like to look at and automatically save the results to CSV or XLS format for plotting or making tables, etc. Setting up the Model Interface to do this is done in one or two steps depending on the level of automation you would like.

First you must set up a “batch query” file. An example of such a file can be found in output/gcam_diagnostics/batch_queries/Model_verification_queries.xml. The idea of such a file is you list the queries you would like to run one after the other and for each query you include the regions (which can be any of the ones listed in the Regions section of the GUI) you would like to query.

<queries>
    <aQuery>
        <region name="USA" />
        <region name="Canada" />
        <gdpQueryBuilder title="GDP by region">
            <axis1 name="region">region</axis1>
            <axis2 name="Year">gdp-mer</axis2>
            <xPath buildList="true" dataName="gdp-mer" group="false" sumAll="false">GDP/gdp-mer/text()</xPath>
            <comments/>
        </gdpQueryBuilder>
    </aQuery>

The actual queries are of the same format as described above and can be copied out of a query file or pasted from the Model Interface.

Users can run this “batch query” file from an interactive Model Interface session by selecting File -> Batch File and selecting the “batch query” file they wish to run. Users are then asked where to save the results (.csv saves as CSV and .xls saves to excel) and which scenarios to run.

Alternatively if users prefer to set up a workflow that does not require any manual user interaction they may prefer to set up a “batch command” file as well (and even collapse the “batch query” to be defined with in the “batch command” itself). An example of such a file can be found at output/gcam_diagnostics/batch_queries/xmldb_batch.xml:

<ModelInterfaceBatch>
    <!-- Note multiple sets of the following are allowed to run several
         batch queries sequentially.
      -->
    <class name="ModelInterface.ModelGUI2.DbViewer">
        <command name="XMLDB Batch File">
            <!-- List all the scenarios to query, if no scenario are given then
                 the last scenario in the database will be queries. Note that if
                 multiple scenarios have the same name the latest one will be used,
                 to differentiate explicitly define the date with date="..." in the
                 scenario tag.
              -->
            <scenario name="Core_Ref"/>

            <!-- The Batch queries file to run.  Alternatively users could specify the
                 queries to run here contained with in <queries> ... </queries> tags
            -->
            <queryFile>batch_queries/Model_verification_queries.xml</queryFile>
            <!-- Where to write results -->
            <outFile>gcam_data/Core/reference.csv</outFile>
            <!-- Which database to query -->
            <xmldbLocation>../database_basexdb</xmldbLocation>
            <!-- Additinoal query options which will be ignored when saving to CSV -->
            <batchQueryResultsInDifferentSheets>false</batchQueryResultsInDifferentSheets>
            <batchQueryIncludeCharts>false</batchQueryIncludeCharts>
            <batchQuerySplitRunsInDifferentSheets>false</batchQuerySplitRunsInDifferentSheets>
            <batchQueryReplaceResults>true</batchQueryReplaceResults>
        </command>
    </class>
</ModelInterfaceBatch>

Users can the invoke the Model Interface from the command line as follows to call their batch file and no user interface will be presented. Note if a batch file named - is specified then the “batch commands” are read from the STDIN. Users can also instruct the ModelInterface to save log output to a file by using the flags -l path/to/log/output.txt.

CLASSPATH=<GCAM Workspace>/libs/jars*:<GCAM Workspace>/output/modelInterface/ModelInterface.jar
java -cp $CLASSPATH ModelInterface/InterfaceMain -b batch_queries/xmldb_batch.xml

3.4.3 Importing data into R

If you use the R programming language to do your data analysis, then you can use the rgcam package to make analysis tasks more convenient. This package provides R functions for extracting results from GCAM databases and importing them as R structures. They take your GCAM output database, along with the same batch query file described in the last section, and run them through the Model Interface, making the results available in your R session for analysis. The imported data is also stored in a project data file for future use.

The rgcam package is available on github at JGCRI/rgcam. Installation and quick-start usage instructions are available on the repository’s front page. Detailed documentation of the functions provided by the package is available through the R help system once the package is installed.

3.4.4 Importing data into python

The gcam_reader python package for importing GCAM data is currently in beta testing. Although not yet as complete as the R package, the python package supports basic functionality including importing individual or batched queries as pandas data frames for analysis or use in other python programs.

3.5 Controlling the level of XML DB Output

The GCAM XML database output is verbose and can consume a lot of disk space. Users may seek to limit or even query and discard these results, particularly when doing a large number of runs, to save space and time. To do this they can configure in <GCAM Workspace>/exe/XMLDBDriver.poperties the following options:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
<comment>Configuration properties to control the behavior of storing GCAM output into the XML database.</comment>
<!-- If the results should put into an in memory database.
     WARNING: this means the data will be lost once the DB is closed.
     This option would be useful if the user wanted to run queries on the results then
     discard them.  Also note that GCAM will still be holding it's memory while this DB
     is created.
-->
<entry key="in-memory">false</entry>
<!-- A timeout, in seconds, to wait in case a user tries to write to an already open DB.
     A negative value indicates to wait indefinately.  Once the timeout has expired or
     a user has pressed any button it will attempt to open the DB once more and if that
     fails again then the results will be lost.
-->
<entry key="open-db-wait">-1</entry>
<!-- The path to an STX style script to filter GCAM results before writing them to the
     DB.  If empty no filters will be applied.
-->
<entry key="filter-script"></entry>
<!-- The path to a Model Interface batch file to run queries after a GCAM run has
     finished.  If a value of - is specified this instructs the Model Interface
     to read the batch file from STDIN which could be useful when being run by some
     other controlling program that wants to dynamically generate the queries to run.
     Note that GCAM will wait to run these queries until after the scenario
     has cleaned up it's memory to create more space for the Model Interface and to
     ensure all results (including cost curves) are available.  If empty no queries
     will be run.
-->
<entry key="batch-queries"></entry>
<!-- Redirect the log messages from running batch queries to the specified log file.
     Note that an empty value will keep the messages printing to the standard output.
-->
<entry key="batch-logfile">logs/batch_queries.log</entry>
</properties>

3.5.1 In memory database

Setting this option will instruct BaseX to keep the entire database in memory instead of writing the results to permanent storage. In memory databases can be faster to write and much faster to query. However this will consume much more memory and as soon as GCAM exits the results are lost. As noted above this would only be useful if a user wanted to run a set of queries against the database and save those select CSV (or XLS) results instead of the XML database.

3.5.2 Filtering results

Specifying a filter script will filter the GCAM results as it is produced by GCAM and only ever writing the filtered results. We used the Joost library to do this which is reminiscent of the XSLT standard however imposes some limitations in order to processes XML as it is generated (as apposed to XSLT which needs to store the full results before it can process them which is unrealistic given the size of the GCAM XML results). A good introduction to the concept can be found here

The specification for how to write the filter scripts using the Streaming Transformation for XML (STX) sytanx can be found here

A number of example filter scripts are provided in the GCAM workspace under <GCAM Workspace>/output/queries/filters. As mentioned earlier the syntax is very similar to XSLT where the bulk of the work is done with template filters that match XML using an XPath syntax with the exception the XPath expressions can not look ahead. Meaning for instance that you could not filter a technology by inspecting the value of any of it’s child nodes such as physical-output. The reason for this is STX must be able to process the XML as it is generated and the child XML would not yet been generated. However STX does provide some workaround to accomplish this using XSLT! More specifically it allows you to collect the results at a given node of interest and apply a sub-filter script once all of the XML for that node has been collected and that sub-filter can be written using XSLT which does allow looking ahead in it’s template definitions. An example script which takes advantage of this feature can be found in GCAM Workspace/output/queries/filters/results_2020_to_2035.xml.

3.5.3 Running batch queries

Runs the Model Interface in batch mode if in the configuration a “batch-queries” file is specified. Note that the “batch-queries” will be read and processed as normal “batch command” except that the <xmldbLocation> will be ignored and use the database opened by GCAM instead. If no batch queries file is specified the Model Interface will not be loaded and no queries will be run. Note: batch queries will wait until the last moment for any given scenario to exist before running. This is to ensure any target finding and/or cost calculations have been run an written to the database so that information would be available to the queries.

3.5.4 Using these features on an exported XML results file

The tools that provide these features can be run independently from GCAM via the command line. This can be useful for working with .xml files exported from the XML DB or the debug_db.xml file. A user could programmatically load them back into a new XML DB using any of the aforementioned features. This is done by calling the <GCAM Workspace>/exe/XMLDBDriver.jar directly:

CLASSPATH=<GCAM Workspace>/libs/jars*:<GCAM Workspace>/output/modelInterface/ModelInterface.jar
java -cp ${CLASSPATH}:XMLDBDriver.jar XMLDBDriver --help
USAGE:
   java -cp XMLDBDriver.jar XMLDBDriver --db-path=PATH --doc-name=NAME --xml=FILE
or
   java -cp XMLDBDriver.jar XMLDBDriver --print-java-path

NOTE: If the first form is used, the arguments -db-path, --doc-name, and --xml are all required.
      Options can be abbreviated using any unique prefix, e.g., --db=XXX --doc=YYY -x foo.xml

Option             Description                          
------             -----------                          
--db-path          Path to XML database                 
--doc-name         The unique name to call the document 
                     in the DB                          
--help             Print this message                   
--print-java-home  Print the path to the Java home      
                     directory and exit                 
--xml              The exported GCAM results XML file to
                     load