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General HydroStatics
Ship Stability Software |
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Command of the Week
(New or interesting aspects of GHS that you may not know about) |
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Array Variables
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For users unfamiliar with programming concepts, an array variable is simply a multi-dimensional variable in which multiple values can be stored and accessed via indexing. For example, think of that spreadsheet you're working with: the workspace can be considered a two-dimensional array, where each value in the array is referenced by its row and column index. Not only are arrays a compact way to store data, but they enable efficient algorithms which may be difficult to implement otherwise.
In GHS, array variables are simply a collection of regular user variables with a common prefix. For example, to create a 1x10 "array" one could use: |
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macro make_array
variable %2_%1 / .make_array(10,1)1 "A" |
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...where the macro make_array is being called 10 times, each time incrementing the first parameter (%1) by 1 starting at 1. The second parameter (%2) is the array variable prefix. %1 acts as the index, and is appended to the variable name on each loop to create a unique variable name. If we want to look at our collection of array variables, we might use: |
| variable /list:A_* |
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...which would list all variables that start with "A_", as yet undefined: |
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We can then SET, access, or otherwise manipulate any element of an array by specifying its index as part of its name:
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macro count
set %2_%1=%1 / .count(10,1)1 "A" set A_10={A_6} TIMES {A_7} \\The answer = {A_10}\ |
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But what about higher dimensional arrays? Easy, just append a second index:
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macro make_array2
macro make_column variable %3_%%92_%%91=%4 // macro make_row .make_column(%2,1)1 %%91 // .make_row(%1,1)1 / .make_array2 6 7 "A" 0 `6x7 array "A" initialized to 0 |
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But what about matrix operations, like Gaussian elimination and LU decomposition? Not as easy, but we've done it. Just let us know if you're brave enough to try it too. |
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Questions, comments, or requests?
Contact Creative Systems, Inc. USA phone: 360-385-6212 Fax: 360-385-6213 Office hours: 7:00 am - 4:00 pm Pacific Time, Monday - Friday Mailing address: PO Box 1910 Port Townsend, WA 98368 USA Click here for an index to this and previous COWs |