Mathematical expressions can be entered in a variety of places in XSIM. The constants and functions that may be used in these expressions are given below.

Constant name	Value	Type	Comments
pi	3.1415...	double	Calculated as 4*atan(1)
e	2.7182...	double	Calculated as exp(1)
eps	~10^(-7)	float	Machine-dependent relative error (See note)
deps	~10^(-16)	double	Machine-dependent relative error (See note)

Note: eps and deps are the smallest values for which (1+eps) or (1+deps) is not equal to 1.

Function name	# of arguments	Aliases	Comments
abs	1		absolute value
acos	1	arccos, arccosine	inverse cosine (|arg| <= 1)
asin	1	arcsin, arcsine	inverse sine (|arg| <= 1)
atan	1	arctan, arctangent	inverse tangent
atan2	2	arctan2	inverse tangent(y,x)
bound	3		bound(lo,x,hi) returns lo<=x<=hi.
cos	1	cosine
cosh	1	hyperbolic cosine
erf	1		error function
erfc	1		complement of error function
exp	1		exponential
fract	1		fractional part of argument
int	1		integer part of argument
isdef	1	isdefined	isdef(x) returns TRUE if x is defined
log	1	ln	natural logarithm (arg > 0)
log10	1		base 10 logarithm (arg > 0)
log2	1		base 2 logarithm (arg > 0)
max	>0	maximum	maximum of arguments
min	>0	minimum	minimum of arguments
mod	2	modulo	remainder (double, real, int arguments)
pow	2	power	pow(x,y) = x**y (all numeric arg types)
ran	0	rand, random	pseudo-random number from 0 <= x < 1
sin	1	sine	sine
sinh	1		hyperbolic sine
sqrt	1		square root (arg > 0)
tan	1	tangent	tangent
tanh	1		hyperbolic tangent

The evaluator permits conditional expressions in a format which is familiar to C programmers:

      expression_1 ? expression_2 : expression_3

When the expression is evaluated, expression_1 is evaluated first. If it is true (non-zero), the expression is assigned the value resulting from the evaluation of expression_2. If expression_1 is false, the expression is assigned the value resulting from the evaluation of expression_3.

For example, the expression:

      Fp > 3.0 ? PSg : PSpc

is assigned the value of PSg when Fp is greater than 3.0 or PSpc otherwise.

Copyright 1995-1998, University of Washington

Last modified: 01:22pm PDT October 17, 1998