Fcn.md

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