.HELP:
This routine allows for generation of a digitized single-variable curve
or two-variable plane from an arbitrary mathematical function in the form
of z=f(x,y), where z represents an array or a grid of function values to 
be computed at NX and NY different points of x and y (equally spaced only)
from a user specified x and y space (XR and YR fields in the dialogue menu).
When entering the f(x,y), use letter X and Y to denote the independent 
variables in the formula of FORTRAN conventions.

To compute a 1-D curve, you can use either X variable or Y variable, then
specify NX and XR or NY and YR accordingly, and results are written to the
file on dialogue field DF in a binary data format for X,Y PLOT. To compute
a 2-D plane, use both X and Y variables and the results are written in the
binary data format for CONTOUR PLOT.

Example: FZ = C0 + C1*EXP(-(X-C2)**2) + C3*COS(2*PI*X) + C4*SIN(4*PI*X)
Example: FZ = C1*EXP(-(X-C2)**2) + C3*COS(2*PI*Y)

where C0,C1,C2... are constants to be specified on dialogue fields C0,C1,
C2,... and a number of mathematical and physical constants are built in.
Max 5 lines (385 characters) can be entered for f(x,y) and they are case-
insensitive. After you have entered one line of f(x,y), the cursor will 
be positioned at the beginning of the next input line.

Defined dialogue commands:

    GO ....................... Start computing the f(x,y) if given.
    EXIT/PF3 ................. Exit from Function Plot.
    HELP/PF2 ................. Invoke the on-line help.
    REFRESH/PF1 .............. Refresh the dialogue menu.
    DCL/PF4 .................. Spawn a system subprocess.

FORTRAN mathematical operators:

    +  ==>  Addition                 /  ==>  Division
    -  ==>  Subtraction             **  ==>  Exponentiation
    *  ==>  Multiplication          ()  ==>  Parentheses

The precedence of operators: () => ** => *,/ => +,-.

Some FORTRAN intrinsic functions:

    SQRT(P1) = Square root          SIN(P1)  = Sine
    EXP(P1)  = Exponential (e)      ASIN(P1) = Arc Sine
    LOG(P1)  = Natural Logarithm    COS(P1)  = Cosine
    LOG10(P1)= Common Logarithm     ACOS(P1) = Arc Cosine
    TAN(P1)  = Tangent              SINH(P1) = Hyperbolic Sine
    ATAN(P1) = Arc Tangent          ABS(P1)  = Absolute value(Real) 
    TANH(P1) = Hyperbolic Tangent   IABS(P1) = Absolute value (Integer)
    COSH(P1) = Hyperbolic Cosine    MOD(P1,P2)=Remainder (P1-P2*(P1/P2))
    INT(P1)  = Truncation           MAX(P1,P2,...)= Maximum among P1,P2,... 
    NINT(P1) = Nearest integer      MIN(P1,P2,...)= Minimum among P1,P2,...

Note: All trigonometric functions demand the arguments in radians.

Built-in mathematical and physical constants:

    PI = 3.1415926E+00  -----------  pi
    DR = 1.7453292E-02  -----------  Degree to Radian Conversion
    NA = 6.0220450E+23  -----------  Avogadro constant
    KC = 1.3806620E-23  -----------  Boltzmann constant (J/K)
    CC = 2.9979246E+10  -----------  Speed of light (cm/s)
    EC = 1.6021892E-19  -----------  Charge of proton (Coulomb)
    EA = 4.8032500E-10  -----------  Charge of proton (ESU)
    BM = 9.2740780E-24  -----------  Bohr magneton (J)
    HC = 6.6261760E-34  -----------  Planck constant (J s)
    FC = 9.6484560E+04  -----------  Faraday constant (Coulomb/mole)
