Parameter Operators and Functions

The built-in functions are:

Abs(x)

Absolute value of x

Acos(x)

Principal value of arc cosine of x

Asin(x)

Principal value of arc sine of x

Atan(x)

Principal value of arc tangent of x

Atan2(x,y)

Principal value of arc tangent of y/x

Ceil(x)

Smallest integer greater than or equal to x

Cos(x)

Cosine of x

Cosh(x)

Hyperbolic cosine of x

Env("s")

Import environment variables

Exp(x)

Exponential of x

Floor(x)

Largest integer not greater than x

Log(x)

Natural log of x

Log10(x)

Base-ten log of x

Max(x,y)

Maximum of x and y

Min(x,y)

Minimum of x and y

Mod(x,y)

Remainder of x/y

Pow(x,y)

Value of x raised to the power of y (equivalent to x^y)

Sin(x)

Sine of x

Sinh(x)

Hyperbolic sine of x

Sqrt(x)

Square root of x

Tan(x)

Tangent of x

Tanh(x)

Hyperbolic tangent of x

The built-in variables are:

E

2.7182818284590452

PI

3.1415926535897931

EPS

Machine precision, typically 2.2204460492503131E-16

The expressions are evaluated at the time they are encountered in the input file; they are then replaced by their values. The expressions are not transferred to restart files; only their values are. For integer parameters, the final value is converted to an integer. For example,

ASSIGN {
    variable                   = SHIFT
    value                      = Sin (PI/8 + Asin(.3) )
}
MULTIPLIER_FUNCTION( "shifted half sin" ) {
    type                       = cubic_spline
    curve_fit_variable         = time
    curve_fit_values           = {  0.0, SHIFT + Sin(0.0*PI) ;
                                    0.1, SHIFT + Sin(0.1*PI) ;
                                    ...
                                    1.0, SHIFT + Sin(1.0*PI) ; }
}

The special function Env is used to import the value of an environment variable and assign it to a parameter, of any type. Environment variables are typically set at the shell prompt prior to executing a command. The syntax of setting an environment variable depends on the shell and operating system. For example, in a Unix cshell an environment variable is set using the setenv command:

cshell-prompt> setenv INLET_VELOCITY 20

The input file may then contain

SIMPLE_BOUNDARY_CONDITION( "inlet" ) {
    ...
    x_velocity = Env( "INLET_VELOCITY" )

The Env function is particularly useful for performing parametric studies. For example, an investigation of the effect of inlet velocity may be automated with the following cshell loop:

foreach vel ( 5 10 15 20 )
    echo "Processing velocity " $vel " ..."
    setenv INLET_VELOCITY $vel
    acuRun
    acuTrans -out -to stats > STATS.$vel
end

The operator "." may be used to concatenate strings. This is particularly useful in connection with an Env function. For example, you can define the PROBLEM environment variable with the following command in a bash shell under Linux:

bash-prompt> PROBLEM="channel"

and then use it in the input file as

COORDINATE {
    coordinates = Read( Env("PROBLEM") . ".crd" )
}

This is equivalent to

COORDINATE {
    coordinates = Read( "channel.crd" )
}

There is significant potential for confusing this operator with the string ".". It is important to be very careful with the quotes. A slightly more complex example equivalent to the above is

bash-prompt> EXT="crd"
COORDINATE {
    coordinates = Read( Env("PROBLEM") . "." . Env("EXT") )
}