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# Fcn
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This module is used to include a user defined in-line (math) function in a
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model.
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Usage:
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The module supports a number of different types of mathematical functions:
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- Polynomials.
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- Non-polynomial combinations of variables and constants.
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- Sines and cosines.
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- Floating-point absolute values.
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- log10.
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- Square root.
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- Combinations of the above.
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Operation:
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When using this module, place it in the model window and connect the
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desired number of input variables via a Mux and one output that will pass
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on the resulting value from the (user defined) function. Double click on
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the Fcn icon and enter the desired function in the Expression field. The
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first (top) input variable to the Mux is defined as 'u[1]', the second
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input variable (from the top) is defined as 'u[2]', etc. (please note the
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square brackets). The user defined function can consist of any combination
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of terms made up of constants multiplied with variables, sine and/or cosine
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functions, floating-point absolute values, log10 values, and/or square
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roots.
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Once the function has been defined, click on OK and the function will be
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incorporated into the model. Please note that it is up to the user to
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ensure the validity of entered functions and values, e.g., only positive
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values for logarithms, no negative values for square roots, no divisions by
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zero, etc. Also, sine and cosine values should, by default, be given in
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radians. If angles in degrees are desired, replace 'sin' with 'sindeg' and
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'cos' with 'cosdeg'.
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In order to include polynomials, a special technique must be used. This is
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best explained with an example. Let's assume the following polynomial
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should be used:
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Out = 2.0 * In1 + 3.5 * In2 ** 2 + 5.0 * In3 ** 3
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This would require a Mux with six inputs. In other words, the first input
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variable ('In1') is connected to the first input to the Mux ('u[1]'), the
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second input variable ('In2') is connected to the second and third inputs
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to the Mux (and will be referred to as 'u[2]' and 'u[3]' in the function
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expression), and the third input variable ('In3') is connected to the
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fourth, fifth, and sixth inputs to the Mux (referred to as 'u[4]', 'u[5]',
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and 'u[6]', respectively). |
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