To modify the array limits for the model, the user must first edit the appropriate PARAMETER values in the MAIN1.INC file for that model. Once the array limits have been customized to a particular application's needs, then the entire model must be recompiled and linked (see Section 4.2.1 above). Because the high value arrays in the ISCST model are 5‑dimensional arrays (NREC,NVAL,NGRP,NAVE,NTYP) and there are three arrays with these dimensions (the sorted high values, the data period for each value, and the calm and missing value flag for each value), the model's storage requirements are particularly sensitive to increasing the number of source groups or the number of high values to store at each receptor location. For example, the amount of storage space required to store these three arrays with the initial PARAMETER values for the DOS version is about 72K. To increase the number of source groups from 2 to 4 would double the storage requirement, adding at least another 72K to the load size of the model.
The user should first determine the types of applications for which they most typically use the models, and then modify the appropriate PARAMETER values accordingly. If someone never (or very rarely) uses variable emission rate factors, then modifying the NQF parameter could free up some memory. Changing NQF from 24 to 1 will free up about 9K for a model using 100 sources. The user may also wish to reduce the NPDMAX parameter if particulate categories are rarely used.
Often, when a larger number of source groups has been used with the ISCST model, it has been for the purpose of performing source contribution (or source culpability) analyses. Since the ISCEV (EVENT) model provides this type of information without having to specify a separate source group for each source, the need for large numbers of source groups in the ISCST model should be lessened. If the storage limits available on the 640K PC environment are too restrictive for particular applications, then the user should examine the possibility of using a different hardware environment or a different operating system where the 640K barrier will not be limiting. Such systems are available for PCs with 80386 and 80486 processors. The extended memory (EM) versions of the models provided on the SCRAM BBS require an 80386 or 80486 processor with at least 8 MB of RAM (7 MB of available extended memory) for the Short Term model and at least 4 MB of RAM (3 MB of available extended memory) for the Long Term model. The setup and application of the models on the DEC VAX minicomputer and the IBM 3090 mainframe computer are also described in the next section of this User's Guide, and in more detail in Volume III of the ISC User's Guide.
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